Learn Hardcore Spanish (Latin America): Creo que en unos años habré desarrollado suficiente fortaleza para hablar en público sin tanta inseguridad. - I think that in a few years I will have developed enough strength to speak in public without so much insecurity.

In Spanish, affirmative creer que (to believe that) normally takes the indicative, because it expresses that the speaker sees the statement as real or likely:

Creo que mañana hará frío.
I think it will be cold tomorrow.

You use the subjunctive after creer when you negate it, question it, or show doubt:

No creo que mañana haga frío.
I don’t think it will be cold tomorrow.

In your sentence:

Creo que en unos años habré desarrollado suficiente fortaleza…

you’re expressing confidence in that future situation, so the indicative (future perfect) is correct.
If you said:

No creo que en unos años haya desarrollado suficiente fortaleza…

then you’d use subjunctive (haya desarrollado) because you’re expressing doubt or disbelief.

Why is it "habré desarrollado" (future perfect) instead of just "desarrollaré" (simple future)? Are both grammatically correct?

Both are grammatically correct, but they express slightly different nuances:

Desarrollaré suficiente fortaleza…
→ I will develop enough strength…
Focus: the process in the future.
Habré desarrollado suficiente fortaleza…
→ I will have developed enough strength…
Focus: by that future time, the process will be completed and the result will already be true.

In context:

Creo que en unos años habré desarrollado suficiente fortaleza…
Emphasizes: By that point a few years from now, I’ll already have reached that level of strength.

If you say:

Creo que en unos años desarrollaré suficiente fortaleza…

it’s still fine; it just sounds a bit more like a general prediction, without strongly highlighting the idea “by that time, the development will already be complete.”

What is the tense "habré desarrollado" called, and how is it formed?

"Habré desarrollado" is the future perfect in English, and in Spanish it’s called futuro perfecto or futuro compuesto.

It’s formed with:

future of haber + past participle

For desarrollar:

yo habré desarrollado
tú habrás desarrollado
él/ella/usted habrá desarrollado
nosotros habremos desarrollado
vosotros habréis desarrollado (mainly Spain)
ellos/ustedes habrán desarrollado

Use it to talk about an action that will be completed before a specific point in the future:

En dos años habré terminado la carrera.
→ In two years I will have finished my degree.

Your sentence fits this pattern: in a few years, that personal development will already be done.

Could "en unos años" be replaced by "dentro de unos años" or "en algunos años"? What’s the difference?

All three are understandable, but they have slightly different feel:

en unos años
Very common and natural. Means “in a few years” / “in some years’ time”, vaguely.
dentro de unos años
Also very common. Adds a bit more of a “within” / “from now until then” nuance, but in practice it usually means the same as en unos años.
en algunos años
Grammatically fine, but less common in everyday speech for this meaning. It can feel more formal or a bit more like “in several years” rather than just “a few.”

For everyday Latin American Spanish, the most natural options here are:

Creo que en unos años…
Creo que dentro de unos años…

Both are good; “en unos años” is slightly more neutral and very typical in speech.

What does "fortaleza" mean in this sentence? Is it physical strength, or can it mean emotional strength? Could I say "confianza" instead?

In this context, "fortaleza" refers to inner / emotional strength, not physical strength. It suggests:

resilience
emotional stability
mental strength to handle a stressful situation (like public speaking)

So here:

suficiente fortaleza para hablar en público sin tanta inseguridad
≈ enough inner strength to speak in public without so much insecurity.

You could definitely use "confianza" instead, and it might even sound more common in everyday speech:

suficiente confianza para hablar en público
= enough confidence to speak in public.

The nuance:

fortaleza: more about overall inner strength / character.
confianza (en mí mismo): more directly about self‑confidence.

Both are correct; the original just has a slightly more “serious” or “psychological” tone.

Why is it "suficiente fortaleza" and not "fortaleza suficiente"? Where does suficiente usually go?

The adjective "suficiente" most naturally goes before the noun:

suficiente dinero
suficiente tiempo
suficiente fortaleza

You can put it after (fortaleza suficiente), but:

Before the noun: sounds more neutral and common.
After the noun: often sounds more formal, emphatic, or written.

Compare:

No tengo suficiente paciencia. (Very natural)
No tengo paciencia suficiente. (Also correct, slightly more marked / emphatic.)

So "suficiente fortaleza" is the most typical word order in everyday speech.

Why is it "hablar en público" and not "hablar al público" or "hablar con el público"?

They express different ideas:

hablar en público
= to speak in public / to do public speaking (the activity itself, in front of people).
hablar al público
= to speak to the audience/public (directing your speech to them). Focus on the addressee.
hablar con el público
= to speak with the audience (more like an interaction or conversation with them).

In your sentence, the idea is public speaking as a situation (standing in front of others and speaking), so "hablar en público" is the idiomatic and correct choice.

What exactly does "tanta inseguridad" mean? Could I just say "mucha inseguridad"?

tanta inseguridad literally = “so much insecurity”
mucha inseguridad = “a lot of insecurity / much insecurity”

The difference is nuance:

mucha inseguridad
States a large quantity, fairly neutral.
tanta inseguridad
Adds an emotional tone: “so much insecurity (too much, more than I’d like)”.
It often implies excess or frustration.

So:

sin mucha inseguridad = without a lot of insecurity
sin tanta inseguridad = without *so much insecurity* (implies that right now you feel a lot, and that’s a problem).

In this sentence, "tanta" nicely conveys how heavy and excessive the current insecurity feels.

Could I say "para poder hablar en público" instead of "para hablar en público"? Is there a difference?

Yes, you can say both:

para hablar en público
= in order to speak in public.
para poder hablar en público
= in order to be able to speak in public.

"Poder" adds a nuance of ability / capacity. The meaning in context is almost the same, but:

Without poder: focuses on the goal itself (speaking in public).
With poder: emphasizes having the ability or feeling capable of doing it.

Both versions are natural in Latin American Spanish; the original is simply a bit more concise.

Can I move "en público" or "sin tanta inseguridad" around? For example, is "para hablar sin tanta inseguridad en público" also correct?

Yes, there is some flexibility in the word order of these adverbial phrases. These are all grammatically correct:

para hablar en público sin tanta inseguridad
para hablar sin tanta inseguridad en público

The usual and clearest version is the original:

para hablar en público sin tanta inseguridad

because:

hablar en público is a very fixed combination (almost like one chunk: to do public speaking).
Then sin tanta inseguridad naturally describes how you want to do that speaking.

If you say “hablar sin tanta inseguridad en público”, it’s still fine, but it slightly separates en público from hablar, so it can sound a bit less smooth, especially for learners. Native speakers do sometimes say it that way in fast speech, though.