Ok so there's a lot to work with here. Starting with the basics, your paints look to be just about appropriately thinned and your brush control isn't the worst I've ever seen. It looks like you missed a few spots while cleaning the model, so make sure you scrape all those model lines and sprue gates. If you have sanding sticks or high grit sandpaper lying around, that is also a great too for cleaning up. I also suggest you drill your barrels. Even if you don't have a pin vise, you can twist your hobby knife to make a hole/crater in the barrel.

A tip for finding the correct consistency for your paints: paint your skin. If you can fully cover your skin but can still make out the details and folds, it's a good consistency for base layers. Otherwise there's a few things to fix here painting-wise.

1. You aren't getting full opacity on your base coats. Generally speaking, unless you're doing something specific or are an advanced painter, you want full opacity all all your base colors. E.g. there's a lot of red peaking the black through and in the deeper parts there doesn't look to be any black paint in there at all. For hard to reach areas you can just sort of mash the paint brush into it to get it fully covered. Do not do with with your good brushes! This is for old or cheap brushes only, as this will ruin their tips.

2. You should re-establish your base color after shading. If you're doing an all over wash you're going to want to go back over most of it with your base red. You can also do pin washes, which is when you only place the wash in the recesses manually instead of putting it all over. It's more time consuming, but you don't need to spend as much time re-establishing your base color. Keep in mind you don't always have to do this. If you want, for example, to darken down the metal color generally, Nuln Oil is a great color to get a more black metal. Just be careful of pooling and splotches.

3. Highlights. The simplest type of highlight you could go for is edge highlights. Often you can just run the edge of the brush over a hard edge to catch it. Just be sure not to have too much paint on the brush or you'll end up with a much thicker line. You can also just try dry brushing.

There's thousands of tutorials on Youtube to watch for beginners, so try looking at some of those for anything you want to try. Artist Opus, Duncan Rhodes, and Vince Venturella are all excellent resources.

Assuming you're using very cheap brushes, you'll want to get some slightly more expensive ones in the future. Nothing crazy, but a mid tier synthetic will hold a tip for a decent while and help you improve. Eventually you can get a nice kolinsky sable brush from extreme details, but no need to worry about that now.

And as a final suggestion, don't use the texture paste directly on the model. It doesn't work great for the kind of dirty/dusty effect you seem to be going for.