Creative drive, I'd say. Some people simply like making stuff

My first kit was the High Grade Gundam Age-1 Normal. Nothing special really, but fun to build. As for what I'd recommend: either a suit you like from the anime, or just one you like the design off.
and a Tip: the newer the kit, the better it (usually) is.

The first anime I ever watched was Pokemon, but I don't really count that, as I had never even heard of the word "anime" back then. My actual first was Mahou Shoujo Madoka Magica. It's still one of my favourites to this day.

Great that you're getting into gundam! As to when you can start with gunpla: whenever you want! I built my first kit before I even watched a single episode of anything

My favourite this season is Mobile Suit Gundam: the Witch from Mercury, with Oshi no Ko and Konosuba as close second and third, respectively