1. sure, transporters should get shot on too. But there is one thing to remember: bombardments take up the whole turn time between turns, i.e. 2 years to 2 weeks (early and late-game) whereas troop transporter just fly in momentarily, deliver troops and get out of firing range of orbitals quickly (then get back to redeploy troops elsewhere according to the needs of the different battle sites) so their exposition to orbital defense fire is way less than the one by orbital bombarding capital ships that fire their arsenals a lot longer on the surface. I'm not really quite sure how to handle this in terms or realism and playability.
One thing's clear, the AI does not build troops yet so they are virtually defenseless against invasions. A human player would probably be a lot more of a challenge. I think the solution will be that there's a possibility later on to do hit&run battle maneuvres targeted on their transporters only, i.e. when defending a planetary system with a fleet you get the option to take out the attacker's transporters first and then either retreat or fight the rest of their fleet. So this is something for tactical combat options to be implemented later-on. For now I suggest not using invasion tactics against the AI, just with human opponents in MP games.
2. sure, but I think that's just necessary. Otherwise you would always know that if you met the Brane, you'd get a >30+ planetary system. If it was less than 30 then you'd have probably a lot of fun trying to build a size 3 ship with a 16 bn planetary system with probably no more than 12 factories and an IP output resulting in build times >20 turns minimum for just one ship. I think weighing up both things the latter weighs more than the first.
3. sure you can do that but are those credits worth it in the end? Usually your opponents should be challenging enough to make you reinvest your money instantly in buying the more-modern ships and buying modern ships usually costs a lot more than 2000 credits. You get 50-75% of invested IP back as credits and the same amount as resources when scrapping at a planetary system (except for deritium which is lost). So you loose all your deritium invested in the ships and get no credits return for the deritium so scrapping is usually not very exploitable because of the deritium shortage you have in nearly every game.
I agree though with end-game resource prices. They should get adapted quicker than at start. I think price development in the early game is okay, but late-game needs to take increased productivity into account. Also prices should not go normal again one turn after a big sell-out for example. They should stay low for a longer period of time because of the "flooding".
Troops are not fully implemented yet. The Alpha Invaders are just experimental "one-time" troops SirP added for the Cartares.
Monopolies will be a victory condition later-on once they get implemented (right now it's just an endless game every time). They are interesting for the Heyoun Trade Union for example. Right now they just let you gain some interests on transactions made by other empires on their stock exchanges like 15% or so. That accounts for the different incomes you gain each turn. Depends on how much the other races are using their stock exchange.
thanks for the compliment