For minor detailing--which is the main fun after building and probably what you mean--I'd say simple
Panel Liner Gundam markers. Use black for dark colors (like black or blackish blue). Use gray for white and most everything else. Brown for yellow or orange colors typically but it's up to you. Panel Liner markers are fantastic, lasts quite a while
(the markers I mean, their applications are perfect and will stick mostly forever in a crevice), easy to use, non-toxic
(unless you lick it off your finger) and are the cheapest of any detailing tool you'll ever purchase. Even when the tips get frizzy or start to break you can still use them like shaders as they then give a kind of smokey aesthetic. Great stuff and pretty universal for ages in application. Shouldn't be more than $10-15 with shipping and tax.
Tamiya spray paint if you want to go for a full recolor of the kit OR if you just want a top coat for some reason. 100% Nothing else compares. The finish, the longevity, the beautiful way it hugs neatly to every minute crevice, it's all just so good. But get the TS series ones since any other is supposedly dangerous or something for Gunpla plastic (I used it on a Kotobukiya kit and haven't seen issues yet but still, better safe than sorry).
Acrylic paint markers are really good and cheaper, too, but if you don't use a top coat (like Tamiya Pearl Clear or Matte (matte is magic but spray it lightly with multiple coats after panel lining) they start to wear easy. They're good replacements for sticker decals on HG kits, though.
But they're not as great in coverage as sprays, but they are less toxic than sprays. Gundam Paint Markers, particularly the metallic ones, are the worst and dim or run if you use any kind of top coat on them. I hear primer can help with that.
But you don't need primer. You're not jumping into big league paint jobs like some of the Admirals in this thread. You're just an Ensign, like me, so don't do what I did and instead just stick to Panel Lining and simple top coating until you get the urge for spray paints or markers or whatever.
Also don't boil your kit.