You DEFINITELY need a basecoat, it helps prevent staining and if you get a good one it will make a world of difference in how long your mani lasts. I love OPI basecoat and CND sticky base coat. Top coats are a must too, and I defintely suggest Seche Vite for fast dry and Nubar Diamont for a regular top coat. The Nubar makes my nails SOOO perfect feeling/looking. I LOVE it.
And then as far as smudging goes can always use ORLY smudge fixer or you can just gently rub the polish when it's still tacky and it will go back into place and then once the top coat is over it it's hard to notice... I do that when the smudge isn't too bad, if it's too deep it's hard to fix.
Colors! My favorite! I think everyone needs the basics of course, and as someone mentioned Sinful Colors is a great cheaper brand to get your ROYGBIV out of the way. I think the best red is China Glaze Ruby Pumps. My favorite blue is Zoya Zuza, it's a bit darker in person and another favorite blue of mine is Essie Butler Please, suuuuper pretty. And then I think everyone needs glitters, a fabulous glitter than is being discontinued is China Glaze Fairy Dust, it's small and adds pop to anything. I also LOVE indie polishes... A great website for them is Llarowe, I've gotten tons of my favorite polishes from there. OH and Model City on Etsy has FABULOUS colors!
I didn't mean for this to be so long, sorry! Hope it helps though!! :)