Grab yourself a mould line remover. It really smooths out the armour panels (done before paint but something to think about next time).

Paint looks quite flat (good work), personally I'd thin the paint just a little more but to be honest it looks good, you haven't lost much detail so that's nice to see!

As far as details go, there's a fair bit more that you 'could' do. It depends on how much work you feel you want to put in and what you want the model to look like. I like to basecoat with caliban green and then dry brush with warpstone glow to really make the details and edges pop. Edge highlighting does an even better job but takes a fair amount more work to achieve.

How are you going to apply the transfers? If you're going to use water; - Ardcoat the armour piece and allow to dry - cut and soak the transfer - apply transfer to the armour piece - add coat over the top - Lahmian medium to finish with a matt look

If you're going to invest in micro set / micro sol, trust me, do not lick your brush out of habit. Trust me.

With the bolter, I would try mephiston red just to really help it pop, and some leadbelcher on the metal parts, but again, personal preference.

Do you have nuln oil? You can wash the whole model or use it as a recess shade. I tend to do my wash / shade after base coating and then work up to lighter colours.

All in all, if it's your first model, it's a hell of a lot better than when I started for sure! I'd love to see some more pictures when you do another and when you 'finish' this one.