Learn Turkish: İnşallah yarın gelirim. - Hopefully I will come tomorrow.

In Turkish, the aorist tense (geniş zaman) is not just for habits; it is also used for future actions that are promises, guesses, or not 100% certain. Because the speaker is using İnşallah (hopefully), the plan is not definite. If it were a guaranteed, scheduled plan, they would use the future tense: geleceğim.

Can I use the present continuous tense (geliyorum) here since it is happening tomorrow?

You can say Yarın geliyorum (I am coming tomorrow) if it is a completely fixed plan, just like in English. However, because this sentence uses İnşallah, the action is not a sure thing yet. Therefore, the slightly uncertain feeling of the aorist tense (gelirim) fits much better than a fixed continuous tense.

Is the word İnşallah strictly religious?

Literally, it translates from Arabic as "if God wills." However, in modern Turkish, it is used by almost everyone as the standard, everyday word for "hopefully," "let's hope so," or "fingers crossed," regardless of their personal beliefs.