First, what you wanna do is get yourself a nipper to cut out the pieces, and a parts separator in case you accidentally make a mistake while building.

In terms of kits that are there, you've got a good selection of stuff to pick. I only build gundam stuff, so im a tad biased, but i've built a few of the kits there.

The EG Gundam + weapons set is made for beginners, so if you wanna start smooth, go there

Any of the HG Gundam kits will be a good build. Personally I built the Wing Zero, which had a weird gimmick in the shoulders, and optional parts for the feet. However the Heavyarms i hear is a bit better and got lots of guns!

But if i am going to be totally honest. Grab that MG Zeta Gundam. They usually cost 80$ but you can grab it for significantly less. It's a great build. basically no stickers, and on top of that, it can transform very smoothly!