50Hp you can rent without a license - and yes expensive from places like Sirmioni and Desenzano, but if you take a ferry to say like Monica del Garda with Rappidrive it is a lot cheaper. Now if you have your ICC you could hire a nice twin 350 horse power sun seeker Great weekend away for your and the other half to get your power boat level 2. But even without, the 50Hp are lots of fun, it is free mooring, and a great way to see a bit of the lake.
Very easy - even better when a lovely Italian lady provides you with the instructions Just stay out of the way of the ferries and you'll be fine. Anything that is on sails has right of way and they will take it. It is a wonderful relaxing way to see part of the lake.
It is out there that we hired out first boat, and then back in the UK went on to get our license, a boat and are now without money left
Seriously, you'll be fine with a little common sense and considering you must enjoy driving on a trip like that then you'll soon get the feel as to when to start turning, slowing down etc. From Moniga del Garda I'll recommend on your first trip to head north along the coast. See the beautiful Isola di Garda. if you are still enjoying it, then go across the water to Salo or Barbarano. Or if you are adventurous go to the other side (but to be fair in a 50Hp outboard it is a little bit of a track).
I'd turn back into the bay and see the beautiful Isola di San Biagio (can only get there by boat), beach the boat and have some nice lunch in the cafe on there. You either swim or get there by boat. Cool location.
Going the other way to Desenzano or Sirmioni is much more busy with ferries, more difficult to moor up. I wouldn't recommend that for the first time.
Anyway some food for thought to do something different