I'm a major economist
Although it's tempting to research trade ports early on, avoid that temptation. Colonizing new planets costs less than establishing an fledgling trade system, and you'll earn a lot more money. As a rule of thumb, ensure you can build a trade port chain of at least length 3 (preferably 4) before you invest in these expensive structures. The longer your chain, the more money each trade port will bring in.
I'm a TEC exclusive.
It's my personal belief that it's actually easier to learn a game by playing multiple factions. This gives you a better sense of what every faction is capable of, and allows you to understand first-hand their strengths and weaknesses.
I NEVER spam, my fleets are always balanced, with a slight lean toward carrier power
That's not a bad thing at all. That said, you may want to experiment with different proportions of units. Try a LRM/flak heavy combination, or a carrier (w/ fighters) / Kodiak combination. Also experiment with different proportions of Hoshikos to find the right balance of damage and support for your playstyle.
Early game I'm ALWAYS behind in EVERYTHING. Literally.
Against unfairs, that's not surprising. Fortunately the AI is an idiot. Unfortunately, it's a cheating idiot.
My defenses suck until mid-game (if I make it that far)
The best defense is a good offense. Having a strong fleet to beat off enemy incursions is the best way to keep your empire intact. Beyond that, one of your best defenses possible is the repair bay. This humble structure can keep simple turrets alive long enough to hold out until your main fleet arrives. Having four or five in a tight formation is a great way to buy valuable time, and also serves as a place to repair your fleet after a big battle.
. I build Cap.s in the following order: Sova Carrier, Dunov Battlecruiser, Akkan Battlecruiser, Marza Dreadnought, Kol Battleship, Dunov Battle Cruiser, Marza Dreadnought, Kol Battleship (repeat)
The Sova is a poor choice for first capital ship in most cases. Its embargo ability is awesome, but you have to put it to use early on for it to be worthwhile, since the Sova is otherwise a very weak capital ship. If you don't want to rush, the Sova is the wrong choice for capital ship. On big maps, the Akkan is almost certainly your best choice. This is because you don't need to pay for an expensive colony frigate. The Marza is another great choice, since it can singlehandedly take out strong militia forces and capture well defended terran and desert planets early on. The Kol also isn't a bad pick.
You usually want to pick your capital ships based on your needs at any given moment in time, not a predetermined build order. The Dunov is a great capital ship, but it's not always well suited to your situation. I typically ensure I have at least one Marza, Kol, and Akkan in the long-run, and very rarely get more than 6 capital ships. As a general rule, a few high level capital ships are more worthwhile than many low-level ones.
I'm a MASSIVE Nova Spammer in the late game
If you have enough spare cash to do that and you haven't won the game yet, you're not playing right The Novalith is almost certainly the weakest superweapon. After all, if you have enough money to spam novaliths, chances are your enemy has so much money that losing a planet isn't a big deal anyways (and if he doesn't, why haven't you won already!?). You're almost always better served by making your fleet larger, so save the Novaliths for after your fleet has reached size 2000.
I ALWAYS have to make the most credits, and NEVER upgrade my fleet if I risk losing this title.
As has already been said, avoid the "always" and "nevers". I used to watch the income rankings myself. After all, if you maintain an income advantage in the long-term, clearly your research and fleet size will ultimately be the largest. However, I find the most important advantage to keep is actually colonization. Your economy is ultimately limited by how many planets you control, and maintaining a large empire is the best way to foster a long-term economic lead.
I will often sacrifice my economy early to raise a military and capture more planets. This will ultimately lead to my economy rebounding in the future because of the extra advantage of those planets. It's all about balacing out your short-term needs with your long-term plans.