tamiya & mr hobby 100ml compare to industril 400ml.

so, This depand on the kit size & layer effect u wan, but for MG maximun 1 unit only.

this hobby is not that cheap to begin with

as far as I know, primer are meant for parts that you sanded (like eliminating seam lines) to smooth out the surface or when you're spraying with different colour other than it's original, as an example blue parts painted with red.

if the colour is the same/similiar then I guess you can skip the primer

Newbie here oso...
from my experience,
i only did the top coat and done nothing else.
though i messed up during the coating part and it looks horrible now

but for me i think the top coat is enough already

if want cheap hobby, go fishing laa lol

Off topic:

here's my recently finished MG heavyarms

more pics here

Just remember I got one of those Tomy building on my office desk (and also I currently kept my GM's HGUC RX-178 on my desk also)

Nope. And the GM in my post refers to General Manager. And if you're interested to see my work desk:

Waaah i actually not impress with this kit but the way u remake it make it look so nice man.. Nice job bro.

What tool are you using? If gundam marker, you can clean up any mess using your fingers. Or you can leave it to dry and clean it with enamel thinner (less smearing).