1. Well I thought of that, but how is it different to other civs, really? For every civ your command center is vulnerable early game. But yes, I intended the Droid Control Center to be the most expensive of the command centers, but as I said I'm not thinking too much about prices, which are used to balance things, and that where a unit or building is expensive it should be obvious from it's description. I also said that Trade Fed buildings are fairly tough in general.
2. Good idea. I think I'll do both - though again I'm not speculating on costs. But PK Droids would make sense to be the most numerous starting worker.
3. The Battle Droid promotion (where Super Battle Droids don't earn experience) is to reflect what we see in the movies. We see different ranks of Battle Droid in The Phantom Menace, so I thought we needed different ranks in the game. But also, Battle Droids don't seem to be as single-minded as Super Battle Droids, they seem to have a bit more personality and initiative, more like C-3PO and R2-D2. I theorise that instead of the Droid Control Signal being a single "hive-mind" that instructs all Battle Droids, it instead is like hundreds of separate, remote droid brains. I've come to this conclusion looking at the way the droids interact with each other - they don't operate silently with a single purpose, they need to communicate vocally and physically with each other. As such I think experience would be earned just the same way as for humans, or at least the same way in which Artoo and Threepio learn experience.
4. I thought of that, and it would make for more realism, but that could be taken advantage of, particularly by the Naboo whose Mechs can shoot whilst on the move. This would force the Droideka to keep moving and not be shielded very often.
5. 20 may seem like a lot but don't forget my transports work on population cost. So while it can carry 20 Battle Droids, it can only carry maybe 10 sith and perhaps only six Droidekas.
6. I'm pretty sure the capacity of both the MTT and the Troop Carrier are identical. It looks to me like the Troop Carrier is just a droid rack the same as the MTT, but without the armour of the MTT.
. I thought Wealth would be more appropriate, because Battle Droids probably won't cost Metal to make (Metal is not plentiful enough to be needed for basic Trooper construction). They probably won't cost Wealth either, but it represents them being recycled and adding to the Trade Federation's economy.