some combat questions:

[Leedot]

Outposts have a small amount of defense but it's really only enough to take on one or two destroyers. It's definitely recommended that you deploy some ships / defensive structures to protect them. As for what you can defend them with other than combat ships you have a couple options. 1. Mine Emplacement (T1 Trade) allows you to create a ship that you can move to any location and then convert it to an immobile mine field.
2. If you have both Cruisers (T2 Fleet) and Orbital Defenses (T1 Combat) then you can convert a cruiser into an Orbital Beam Array at an outpost. There's a similar combo with Advanced Orbital Defenses (t2 Combat) and Armed Command (T3 Fleet). It looks like the the description of those combos weren't included in the tech description so I'll correct that in the future versions of the client.

One important thing to keep in mind with how the combat system works is that currently ships can only attack one target per round so a large number of weaker ships can still take down a target with much higher defense / attack simply because the large ship gets worn down while trying to weed through all the smaller ships.

Also, on the front of what you can attack keep in mind that you're not really choosing to attack a specific target so much as initiating war with that player. One you've told your ships to attack they'll attack everything belonging to that player that's in the same planetary orbit. Also after you've attacked someone twice you'll automatically be flagged to 'war' status with that player and your ships will begin fighting automatically when they're in the same place.