I've never done a jam before, is this a good one to start with?

That’s up to you. If you’re good with a 72 hour jam that gives you a random limitation that you have to follow, then its great to start with!

in my opinion i would start with any jams that gives you alot of time like a week or 4 days before submission

I'd say go for it! If you have 3 days time and are willing to experiment with a random idea to get some experience and maybe learn something new.
You can always not submit the game and just follow along for yourself :D Just remeber to take the time to plan and have realistic scope. 

MiniJam was my first jam and I really enjoyed the experience!

in my opinion that depends on the limitation this jam is good for beginners but it could get overwhelming fast for me the sky mini jam was to overwhelming and i dropped out so it's mostly up to you