Dia menyarankan saya menjaga jadwal yang seimbang antara proyek sampingan, kuliah, dan jeda untuk istirahat.

In Indonesian, menyarankan usually takes a direct object (the person) plus a verb phrase, rather than a bahwa-clause.
So:

• Dia menyarankan saya menjaga jadwal...
  = literally: He/She suggested (that) I keep a schedule...

Using bahwa after menyarankan is possible but sounds more formal and normally introduces a statement, not an action you should do. For suggestions about actions, patterns like menyarankan agar saya menjaga... or menyarankan saya untuk menjaga... are more natural than menyarankan bahwa....

All of these are acceptable, but there are nuance and style differences:

1. Dia menyarankan saya menjaga jadwal...
   – Common, fairly neutral, slightly more concise.

2. Dia menyarankan agar saya menjaga jadwal...
   – Also very natural; agar explicitly marks the clause as something desired/aimed for (so that I keep...).

3. Dia menyarankan saya untuk menjaga jadwal...
   – Also common; untuk connects the suggestion to the action, similar to English “suggested me to keep” (though that exact English structure is not standard).

In everyday usage, all three are fine, with (1) and (2) probably the most common in more careful or written Indonesian.

• menjaga jadwal = to maintain / stick to / keep to a schedule. The focus is on continuing to follow the schedule.
• memiliki jadwal = to have a schedule. You possess a schedule, but you might or might not follow it.
• membuat jadwal = to make a schedule. You create it, but again, not necessarily follow it.

In this sentence, the idea is not just having or making a schedule, but maintaining a balanced one over time, so menjaga jadwal is the most natural choice.

In Indonesian, adjectives and many descriptive phrases typically come after the noun:

• jadwal yang seimbang = a schedule that is balanced
• rumah besar = big house

Here, yang seimbang functions like a relative clause:
jadwal yang seimbang ≈ “a schedule *that is balanced”.
Putting *seimbang (through yang seimbang) after jadwal is the standard Indonesian word order.

Indonesian antara can be used with two or more items. It doesn’t have the strict “between = 2, among = 3+” distinction that English has.
So:

• antara proyek sampingan dan kuliah – between side projects and classes
• antara proyek sampingan, kuliah, dan jeda untuk istirahat – between side projects, classes, and breaks for rest

Both are grammatically fine. The three-item list after antara is completely natural.

Basic Indonesian nouns usually do not change form for singular vs plural; proyek sampingan can mean “a side project” or “side projects”, depending on context.
If you want to clearly emphasize plurality, you have options like:

• proyek-proyek sampingan – side projects (reduplication emphasizes plurality)
• beberapa proyek sampingan – several side projects
• banyak proyek sampingan – many side projects

In this sentence, proyek sampingan can naturally be understood as plural, given the context.

In this sentence, kuliah is a noun, roughly “lectures / college classes / university studies”.
But kuliah can function as:

• a noun:
  
  • Saya ada kuliah jam 9. – I have class at 9.
• an intransitive verb (to study at university):
  
  • Saya kuliah di Jakarta. – I study (go to university) in Jakarta.

Here, because it’s in a list after antara (proyek sampingan, kuliah, dan jeda...), it is being used as a noun.

• istirahat by itself usually means rest or to rest (verb or noun, depending on context).
• waktu istirahat = break time, the time allocated for rest.
• jeda = pause / interval / break (more like a gap between activities).
• jeda untuk istirahat = breaks for rest; it highlights the pause (jeda) plus its purpose (for resting).

So the phrase suggests intentional, scheduled pauses for rest, not just the abstract idea of resting.

That version is grammatically possible, but the meaning becomes ambiguous:
jeda untuk istirahat yang seimbang might be read as “balanced breaks for rest”, i.e., yang seimbang now seems to modify only jeda untuk istirahat, not the whole schedule.

By putting yang seimbang right after jadwal:

• jadwal yang seimbang antara ...

it clearly shows that the schedule is balanced across those three components, not just that the breaks are balanced.

• dia = he/she, neutral, used for most people in everyday conversation.
• beliau = a polite, respectful form for he/she, used for people you respect (teachers, older people, officials, etc.), especially in more formal contexts.

So you can say:

• Dia menyarankan saya menjaga jadwal... – neutral.
• Beliau menyarankan saya menjaga jadwal... – more respectful / formal, implying the person has higher status or deserves respect (e.g., your professor).

Indonesian verbs like menyarankan, menjaga do not change form for tense. Context usually tells you whether it’s past, present, or future.
This sentence could mean:

• He/She suggested (earlier) that I keep a balanced schedule...
• He/She is suggesting that I keep a balanced schedule...
• He/She generally suggests that I keep a balanced schedule...

If you need to be explicit, you add time expressions, e.g.:

• Kemarin dia menyarankan saya menjaga jadwal... – Yesterday he/she suggested...
• Tadi dia menyarankan... – He/she just now suggested...

Yes, in casual spoken Indonesian, people often shorten and change some words:

• Dia menyarankan saya menjaga jadwal yang seimbang...
  (formal/neutral)

might become:

• Dia nyaranin gue buat jaga jadwal yang seimbang antara proyek sampingan, kuliah, sama waktu istirahat.

Changes include:

• menyarankan → nyaranin (informal)
• saya → gue (very informal Jakarta-style I/me)
• untuk → buat (informal for/to)
• dan → sama (informal and)
• slight vocabulary shifts like jeda untuk istirahat → waktu istirahat.

The original sentence, though, is good natural standard Indonesian.