Hello and welcome to Tapas! We hope you enjoy your stay here
To answer your questions:
1) At the very least, once a week. You'll lose audience if you don't have a regular updating schedule, so it's best to decide on a day to upload new episodes, then stick to it! More frequent uploads means more views, but really, don't sweat it. (Most people only upload once a week anyway )
2) Weekends. I upload my comic on Wednesdays and Saturdays, but most people only check them out on Saturdays. I've also heard updating around 5-7 p.m. PST is best, since that's the time people get off school and work.
3) Personally, I prefer longer formats. But since your comic is slice of life/comedy, 4 panels will work just fine.
4) I think the art style of your comic is endearing; it's simple but cute. The text is also big enough for mobile readers. Right now, I don't have anything I would want to change about it. Great job!
Good luck on your comic