@Caedus
this is good news, and it's going to be fun to make custom minis!
I am by no means a pro, and what little I've learned, I've learned by asking that same question here in the SWMinis excellent "How-to" thread,
and of everyone at coolminiornot, boardgamegeek, lead-adventure.de and W40K leagues etc.
so, definitely keep on asking questions, and when you get to be "Yoda" of SWMinis, you can 'pass on what you have learned'
SWMinis customs are made of a couple of different vinyls, potentially also resin or other plastics if you're combining parts from several miniatures to achieve the final look - say, Heroclix + SWMinis, or 3D printed + SWMinis, or Wargames Factory etc...
so, you need to stay away from the turps and heavy oil-based paint removers.
why? these'll melt your vinyl miniature.
light acetone like such as in nail-polish remover is sufficient, as acrylic nails are very similar to the plastic some miniatures are made from.
using a cotton-bud or fresh ear-cleaner, you can lightly apply the acetone to the area until the color is removed,
and then rinse the miniature in a clean tepid water bath (inside a dedicated take-away container hehe).
this will usually not discolor your miniature, and will remove ~60-90% of the color.
It's very similar to 8-bit-guy's procedure for retrobrighting actually.
8-bit-guy reverses some of the photo-chromatic yellowing of some plastics.
changing topics to paints;
you can get away with a light primer over the top in a base color, such as GW's Citadel White or Vallejo White.
Tamiya matte white is also a cost-effective option, though ensure it is not the enamel or the other-base white,
as this will melt your vinyl mini hehe.
That can be an adventure all it's own - if you go to a Tamiya ultra diamond retailer, usually located in your local 'china-town' or so,
you can meet folks that assemble gashapon-correctibiru and can recommend various paints for the model etc.
(fun trivia - the Gundam Evangelion micro-series of gashapon correctibiru silver and gold sets were made at the same factory which made our SWMinis run initially)
many gashapon-correcitibiru as by Bandai or Konami etc, they are also in vinyls.
in terms of paints;
Try to stay away from Humbrol or non-name generic acrylic, definitely no water colors or oils hehe
though if you have to use those options, thinner gradual coats are a must,
with a sealant of your choice. Your results will vary, and i cannot guarantee longevity of the miniature or look over time.
enamel may melt your mini. oils and watercolors will flake and chip after a while with handling.
Some Polish and Russian SWMinis fans use 'chalks' and light oil-based paints over their base coat and water-colors even,
and then seal it! it is INCREDIBLE, though, prone to fading or discoloring over time. still,
they can achieve blending effects not quite possible with other colors.
In terms of painting hardware - you'll likely also want some micro-brushes;
a 00 or 000x sizing head, ~0.5mm to 2mm, maybe a Stadler paint pen 0.01mm architectural pen for eyes and ultra-fine details,
and then different kinds of brushes like a 3mm, a 5mm and then sponges or other style for 'drybrushing' or 'weathering' effects.
To start with though, all you'll need is a 2mm fine brush.
You don't need to shell out for ultra-premium brush heads or brand name brushes,
I've still got my first set of brushes and if you clean them after you use them ,they can last a long time
Changing topics to glue and joining or reposing -
usual suspects are regular superglue, 2 part epoxy non-thermal binding araldyte etc - as the ones for joining polypipe and the like will melt your vinyl mini hehe.
it is possible to cut and reposition using an old kitchen knife or a 2 dollar scalpel blade,
and you can use the wire from a paperclip or that comes in twist-ties or from your bread-bag (I don't know how bread comes packaged in your locale, local bakery or corner drugstore type deal usually has bread with twist-ties)
instead of needing to buy a whole special gauge of thin jewelers wire or florist wire.
the wire isn't necessary so much for vinyl models, though it really helps hold the parts together, just a 2mm or so rod and with SWMinis vinyl,
it can be pressed into the vinyl if you have a vice and some pliers.
I hope this helps; I'd rather give you too much of an answer than a non-answer hehe.
and I look forward to seeing what awesome custom miniature you make!
Be sure to check out "The Lost Twenty" guide - some of the first customs and easier ones to make, with a how-to guide and visual step-by-step guide, it's great! there are a few different eras you can make projects in, so it's a great place to start.
Kobayashimaru