[WA]

All of these can be done as sole proprietor (Einzelunternehmer), too.

Bank account: Just go to your bank and create business bank account.

Leftover money: It's up to you how much you withdraw, although you must pay tax on all income minus expenses.

Limited liability is not true (see Geschäftsführerhaftung).

Insurance: Again, you can get insurance (IT-Betriebshaftpflicht) as a sole proprietor too.

I think, if your project is merely ramen-profitable, don't bother about all the organizatorial overhead.

Another downside of a UG/GmbH: More paperwork for taxes etc. (double bookkeeping).