Just got the demo...a few questions

[Suicide Junkie]

For stock, you will want to research projectile weapons early. Level 5 DUCs will be good enough for quite a while, and you can put off researching the more advanced weapons for quite some time.

Using missiles on your ships is good for your first scouts, since the enemy won't have point defense cannons. The missiles won't be effective for very long, so you should switch to DUC warships fairly quickly.

Shields and ship construction are the other two critical stock war techs.
Bigger ships and more hitpoints. You may need to research some physics before the shield tech area becomes available.