I will try to gather here as many tricks and Hints i can find for the game.
1.- How to play story line with any race:
Open your profile with wordpad and find this line:
gametype: 0 and set it to gametype: 1
Now, go to solar system and I think first quest will start. So this is a hack so you can play story with any race 
Clarification, for those that dont know about the game, you can play it in 2 ways, story mode and free mode. In story mode you begin as EMD race and finish with it, in free mode you can choose almost all races...but dont play story line. Well with this trick you can now...
Another hint.
Is there a way to change mian guns in battle? if there is tell me please. if not then why can yiu equip 2 mian guns and 2 missles?
The only way to open the inventory in battle is to change the config.cfg. Open the config.cfg with wordpad in spaceforce2/system and change this line from "EnableInventoryInBattle: 0" to "EnableInventoryInBattle: 1" (without ").
Your other question is easy to answer. Only heay fighters have 2 guns and 2 missles slots.
You can find the heavy fighters here:
Ord_Patrolship (850 upgrade points) find you in the Aguila System, costs 95.800 Credits.
Makkinist_FighterDrone (900 upgrade points) find you in Canis Major System, costs 104.300 Credits.
EMD Valkyrie (800upgrade points) find you in the Caelum System, costs 90.600 Credits.
UF Valkyrie (700 upgrade points) find you in the Serpens System, costs 85.900 Credits.
PS: All Ships find you on the big trade stations in the system.
