TEC is a good choice to start with. Of the three factions, they are the most similar to "us" in how they operate.
There are some very good threads here about the questions you raise...
This one about the first CapShip as TEC:
https://forums.sinsofasolarempire.com/309106
This one about the learning curve and what to do early game: https://forums.sinsofasolarempire.com/307759
And this one about Space Ponies... because they invariably come up every month or so.
https://forums.sinsofasolarempire.com/301293
There are many more, but these should answer alot of your questions. There are also alot in the strategy forum. I would highly recommend going in there and reading. Even the older posts have valuable info in them.
As for mastering the factions... Start on a small random map with you and 2 opponents. In the set up screen, make you TEC and specify the AI to one of each faction. You can set difficulty too, but I would leave them on normal and random. Easy AI is WAYYYY to easy, and they act nothing like they will in a real game. Seeing all of the factions together will help you to see the differences better. I hate the pirates, but they are the best teacher for creating maintaining a fleet. You can always bribe them to go after someone else, but they are pretty predictable... you get a warning and they don't have CapShips, so they can be defended against easily. Well, easier than a race.
As TEC, get 2 civilian research stations up ASAP. Research the ice and volcanic world colonization and TRADE. The order depends on what planets are near you. If no Volcanics, do Trade 2nd... follow? Put a trade port by each planet. Some people spam them, but I limit myself to one to keep it "honest", so to speak. Trade income is your friend...
Play a game or 2 and post again with specifics. There's always someone around to answer, and once they do someone else will disagree and you'll soon have 5 ways to look at any given problem. Nice thing is, they'll all work... you'll just need to see which way suits your play style.
T