I would say priming is almost necessary for a couple of reasons. The plastic is glossy and paint can come right off. Since the pieces do come in different colors, having that uniform color to start will give you a uniform finish also. I primed the armor in light grey and the inner frame with black. A black base works way better for metallic colors.
For painting, I first build the model to see how it all looks together and find where I want my color separation. You do not want to paint while the pieces are still on the runner because you have to trim and sand the nubs for a smooth finish and that can destroy the paint you put on.Then I take off all the armor pieces and keep as much inner frame together as possible. I paint each armor piece individually for best coverage. It can feel like a chore but the results show for themselves
And for a website, the best place I have found would be r/gunpla on Reddit. Instagram can be good, but there is not much discussion happening there.
Since you say you want to get into gunpla, here are some tips I can give. If you just want to dip your feet and see what’s up, buy a High Grade (HG) kit. They are pretty cheap, like 15-20 bucks and do not take long to get together.
Buy a kit that looks interesting to you! Do not feel like you cannot buy a kit because you do not know anything about the mobile suit. There is over 50 years of manga and anime from Mobile Suit Gundam! It’s impossible to know every suit! I have only seen a handful of the shows and usually just buy whatever looks the coolest!
If you want to buy a bigger model with more detail and more pieces, buy a Master Grade, the Zaku 2.0 is one of my favorite designs and it is a fantastic kit when built up.
Since almost all gunpla have articulalation ( arms, legs, head, etc can move) you have to be really careful with your paint job when adjusting the poses. Paint can and will get scraped off in the process, just try and minimize it.
I know this is quite I bit, but I’m pretty passionate about gunpla. If you have any more questions, please ask and I’ll reply the best I can! I hope you dive in and build a kit!