Podemos ir en chanclas a la piscina, siempre que no tengamos que caminar mucho.

Podemos means we can, and it usually sounds more direct and factual.

In this sentence, podemos ir en chanclas... suggests that going in flip-flops is a real option. It can express:

• possibility: it is possible for us to go in flip-flops
• sometimes permission: we’re allowed to go in flip-flops

If you said podríamos, that would mean we could, which sounds a bit more tentative or hypothetical.

So:

• Podemos = we can
• Podríamos = we could

In Spain, chanclas usually means flip-flops or very casual rubber pool/beach sandals.

It is a very common word in everyday Spanish from Spain. In this context, it strongly suggests the kind of footwear you wear to the beach or pool.

Depending on the country, other words may be used, but in Spain chanclas is completely natural.

In Spanish, ir en + clothing/footwear is a very common way to say to go wearing something.

So:

• ir en chanclas = to go in flip-flops / to go wearing flip-flops
• ir en bañador = to go in a swimsuit
• ir en vaqueros = to go in jeans

You might hear con chanclas in some situations, but ir en chanclas is the most idiomatic choice here when talking about what someone is wearing.

Because ir normally takes a before a destination.

So:

• ir a la piscina = to go to the pool
• ir al cine = to go to the cinema
• ir a casa = to go home

Here, a la piscina tells you where you are going.

Because siempre que can trigger the subjunctive when it means provided that, as long as, or on condition that.

In this sentence, the speaker is setting a condition:

• we can go in flip-flops
• as long as we don’t have to walk much

That kind of condition uses the subjunctive, so:

• tengamos = subjunctive
• tenemos = indicative

Compare:

• Siempre que llueve, me quedo en casa. = Whenever it rains, I stay home.
  Here it means whenever, so the indicative is used.
• Iremos siempre que no llueva. = We’ll go as long as it doesn’t rain.
  Here it is a condition, so the subjunctive is used.

Here, siempre que means as long as, provided that, or so long as.

It does not mean whenever in this sentence.

That is an important point, because siempre que can mean two different things depending on context:

• whenever
• as long as / provided that

In your sentence, because it is followed by the subjunctive (tengamos), it clearly has the conditional meaning:

• provided that we don’t have to walk much

This is the structure tener que + infinitive, which means to have to do something.

So:

• tener que caminar = to have to walk

In the sentence, it appears in the subjunctive:

• tengamos que caminar = we have to walk

Broken down:

• tengamos = present subjunctive of tener
• que = introduces the obligation structure
• caminar = infinitive, to walk

And with no:

• no tengamos que caminar = we don’t have to walk

Because mucho is used to mean a lot with verbs.

Here, caminar mucho means:

• to walk a lot
• to walk much

By contrast, muy is used to modify adjectives or adverbs:

• muy lejos = very far
• muy cansado = very tired

So:

• caminar mucho = correct
• caminar muy = not correct here

Yes, in many cases you could say andar instead of caminar.

In Spain, andar is very common in everyday speech. Both can mean to walk, but there can be slight differences in tone:

• caminar can sound a bit more neutral or slightly more formal
• andar is very common and conversational

So no tengamos que andar mucho would also sound natural in Spain.

Because Spanish often leaves out subject pronouns when the verb ending already makes the subject clear.

Here:

• podemos already tells you the subject is we
• tengamos also matches we

So nosotros is unnecessary unless the speaker wants emphasis or contrast.

For example:

• Podemos ir en chanclas... = normal
• Nosotros podemos ir en chanclas... = more emphatic, perhaps contrasting with someone else

Yes. Spanish allows some flexibility in word order.

For example, you could also say:

• Siempre que no tengamos que caminar mucho, podemos ir en chanclas a la piscina.

This means the same thing. The difference is mainly one of emphasis:

• original sentence: starts with the main idea, then adds the condition
• reordered sentence: starts with the condition first

Both are natural.