zazu49: Good Evening,
I'm wondering about how I should garrison my planets in the campaigns and in Galactic Conquest. Do I need both space and land garrisons? What units should I use and how many? Or, should I just rely on the built-in garrisons from buildings and space stations?
-Zazu49
Each of the production buildings has their own sort of unit that it produces. There are a couple of ways you can go about organizing your planets.
1. Specialize, this is what I usually do, build money planets full of mines, and other planets with low or medium income can be production hubs with no more than 2 kinds of factories. This makes production nice and fast and gets you a ton of money, but it makes certain planets really hard to defend without dumping units there.
2. Full on defense. Build a shield generator, turbo lasers and a combination of light and heavy vehicle factories (or advanced when playing empire) and a single barracks there. Dump a good mix of units on the planet itself and nothing short of a deathstar or prolonged assault will take the planet from you. This is usually only viable on planets like Byss, Geonosis and Tatooine that have a large amount of building spaces. You can always skip on the turbo lasers on smaller planets and stuff.
3. Generalize, somewhat like full on defense, but with mining facilities instead of shield generators and turbo lasers.
Space Garrisons are a bit of a special case, usually space battles are more important than land battles, especially if you are playing Empire. But generally having a bunch of ships stationed at a planet makes it pretty buff, although usually a level 5 space station can defend itself quite well, thanks to garrison units.
If you play as rebels, be sure to put an Ion cannon on the surface of your planets, as it helps fight those nasty star destroyers and can even cripple the executor quite well. The Empire Hypervelocity cannons are also nice, but are not that effective in a multiplayer match vs rebels as they will just use raids to skip space battles.
Hope this helps!