Help me build my ship

As you are in a MK2, I guess you are fairly new to the game.
Forget the epics for now, just keep them in inventory, and only once you have 4 duplicates of an item you want to use in the end game, then start to build them up.
For now focus on rares as they are easier to build and will build a solid foundation to work from.
Railgun is hard to use early on as it has a really long cool down, and limited slots on a MK2 will hold you back.
I would be looking to use cannons primarily and stick to what you have the most duplicates of.
Once you have more weapon slots you can benefit from using weapons with long cooldown like the rail gun.
If you send a pic of your inventory, then I will give my advice on what to use

 

Welcome to the bay
If you like the rail gun then stick with it, but keep your other 2 slots as items which require less cool down so you can keep shooting often.
Stick with the shooter, it is probably the most used and most versatile ship, and allows you to use any weapons, and work on multiple weapon achievements at same time.
You do need to start saving big shields and turbos, as they are essential for the end game.
If you want to use railgun, get your buzzkill talent tree maxed, it has a lot of talents to increase power and reduce cooldown.
Also get yourself a good guild, and use the tokens from quests for the raffle, you will get lots of weapon perks and pieces this way, as looks like you dont have any yet?

 

Also spend your stars, you are sitting at 75 stars?!

 

wow you are playing hard bro!!

 

Gattling Gun is certainly a weaker weapon.
Uncommons will become obsolete very soon, so dont waste too much time / resources on them.
Every week you will get free premium chests for logging in every day of the week and for completing all of your weekly quests (18) so very soon you will have plenty of rare gear to work on