Do you collect all products or just a specific variety/generation?
I collect all generations to a degree but my main focus in G1 and I don't add G4 ponies to my collection anymore. With merchandise, playsets, and accessories I'm a lot more picky about what I'll buy but I'd be happy with almost anything as a gift! I'm not a fan of G4 merchandise most of the time, unless its handmade, so I tend to avoid it.
What sort of lines of pony products do you collect?
With G1 and G2 its just everything, whatever I can find. Ponies, merchandise, mommy charms, playsets, accessories, erasers, random household stuff, etc. I like pretty much all of it! With G3.5 I like customs or babies, but I wouldn't turn down a couple regular ponies. With G3 its sort of random, but most brushables and playset/accessory stuff. I kind of like Ponyville but I want to see them in person. I LOVE Ponyville playsets though! As for G4, I mostly keep special gifts, white ponies, and the little animals. I have one playset and that's it. Although i do love blind bag ponies, they got very stale very quickly for me.
Is there a specific pony or ponies you have an army/armies of?
Sundance! :D My main focus is G1 but I'm happy to grab other generation Sundance stuff whenever I get the chance.
What do you find to be easy/challenging about collecting ponies
These days I find it easy to enjoy my ponies. I have okay displays in the process of being upgraded and I actually get to enjoy them instead of shoving them away in drawers. Probably most challenging for me right now is actually getting new ponies. I have a lot of collections to balance and when ponies aren't my #1 priority its really hard to justify things like perfectly fair shipping costs. Its been a few years since I bought a pony for my collection.
What tips would you offer people starting their pony collections
Don't listen to the first cleaning advice you hear. Do a LOT of research before you touch your ponies with anything - water or products. If you get a pony who looks weird, research them. Ask if they need to be cleaned a special way. Don't be afraid to sound dumb or like you're asking silly questions. You're not! Its better to ask a ton of questions instead of accidentally ruin a pony and feel horrible about it.