Acrylic paints

There is a difference between marker peens and paint pens.  I find both are useful.  Some marking pens put down a neat transparent color on glossy material.

My favourite Acrylic finishes are Windsor & Newton Galleria, in Mat, Satin and Gloss, from the Art shops.

I find them the least problematical for me.

Tamiya X range are gloss, Tamiya XF are flat, but the if smell isn't to your liking... 

Hannants XtraAcrylics are acrylics, with a semi gloss sheen, may be hard to get outside the UK though.

Since you have invested in a range of paints, get to know then & get used to using them.

With any experiments using non-brand finishes over (or in) your paint, always experiment on a non-important model, and NEVER mix untested in your airbrush! (Vallejo + IPA/alcohol = rubbery goop!)

Broadly, most acrylics are flat, but your technique & thinning/additive mediums will affect the finish.

You can add gloss/semi gloss to acrylics to increase shine, at the expense of opacity, sometines to get that translucent effect on purpose.

I have used Future with Badger StyNylRes primer, it gave a nice sheen, and hardened the finish against handling as well.

AK''s Gauzy Shine Enhancer or Alclad Aqua Gloss is what I use.

If you can't find Future floor polish (or whatever it is called now) for a gloss coat,  Holloway House Quick Shine - available at Lowes, Home Depot, or many big box stores makes an excellent hard gloss coat.   27 oz for less than 9 bux.

To go with a product with a model manufacturer's logo, AK Interactive Intermediate Gauzy Agent is a good acrylic gloss item.  Small bottles get more expensive.

Scale Colors Paints makes several products in Gloss, Satin, and Matte finish.   They brush (keep a wet edge) and airbrush well

These are all acrylic products.  You can mix your Scale 75 paint with them for your desired level of opacity and gloss

When I want acrylic gloss, I use Tamiya or I clear coat. But there are a few other brands around. I know that Testors square bottle acrylic model paints offers gloss. But have no idea how good they might be.

I actually have used quite a bit of clear coated craft paints. Though lately I've been back on lacquers and enamels.

You can always cover the flat paints with a gloss coat.