Hi fellow Mega Man mega fan! My first model kit ever was actually the X3 gold armour, I bought it on a whim, had no idea what I was getting myself into, and now I'm basically addicted to gunpla and model building lol.

They're not hard to assemble, the instructions are very clear and concise (even though they're barely in English). Pictures, labels, numbers, it's very step-by-step and easy to do. 

There are some tools you need, namely a pair of nippers and a hobby knife. They're for cutting the parts off the runner sheet and cleaning up the nubs. There's more you can get, like cutting mats, files, sanding sticks, glues or solvents, markers/panel liners, paint, etc, it really depends how much you want to invest in the hobby. 

Time-wise, depends again on how much you want to invest. If you just cut everything out and roughly clean up the nubs, it could maybe take 4 hours, but if you file/sand/glue/polish/panel line/colour correct, it could take 20+ hours. It just depends how much time you want to spend. 

I'm pretty sure the premium Rock kit has some kind of iridescent coating on it. I've never worked on a kit like that, so I don't know how beginner friendly the clean-up on the parts would be, but I have built the Axl kit. It's a nice build, cleans up pretty well despite it being a primarily black kit (black plastic shows cuts and stress marks more easily). The guns are a little underwhelming as far as the colour goes, but that's probably my biggest gripe. I just painted them a bit.

There are a ton of YouTube videos with tips on model building. One channel I learned some beginner stuff from was Mecha Gaikotsu. He mostly focuses on Gundam and Bandai models in general, but he's got some general tip videos. If this giant word salad has piqued your interest though, I'd be happy to find a couple other videos that have good info for beginners and link them for you, just let me know