Matt finish and Gloss finish

Depends on the surface detail and the scale you are modeling.  Some model paints (not all) have pigment ground finer than in general purpose paints.  You can certainly use other paints, but it might be harder to get a really thin coat and preserve detail.  On larger models, and ones with little surface detail it does not make much difference.

One club I was in had a contest where the model HAD to be painted with a locally available paint from the hardware store that was well-known for being thick and covering detail. Yet most of the models looked pretty sharp.  This was a model car club, and all the finishes were glossy.

I used Clear Acrylic Sealer-Matte that I got at the AC Moore craft store near me for my latest build and had no problems with it.  Just make sure you use it in a well ventilated area. I have been using a lot of acrylic paints from craft stores. They seem to be working extremely well and are really cheap. Testors Dullcote is $5 for a small can and if you don't have a LHS near you it's $4 shipping. I went into AC Moore and got the Matte Sealer for $7 and it's a large 12oz. can. The paints (almost any color you can imagine) are usually $1 to $2.50 each. Hit a sale once where the paint was 3 for $1. For $10, I got 30 bottles of paint. I thinned the white and light blue for my MIG-3 and used it in my AB. Hope this helps.

Jim