When to use trade, versus orbital, versus population upgrades

A soon as you colonize a world research infrastructure to lvl 2 to cut lost. And you should start laying down trade ports as soon as possible. That normally mean the 2 research labs at your home world will be civic labs.

Refineries are good but only later in game. Early game spam trade ports.

In my opinion, your order early game as TEC should be:

1) Upgrade all colonies so you aren't losing money on them

2) Then do tradeports. However, if you have a volcanic or ice planet close to you, I would research the appropriate exploration before trade ports. Ideally, once you have 3 or 4 planets, you should start laying your trade ports.

3) Refinaries, as was said, are a bit more for mid/late game. Get them when you can but not at the expense of not growing and upgrading your planets and putting trade ports on them.

As was mentioned, the first two population upgrades are essential and need to be done on any planet you take. The ones later are nice, but not as urgent.

In general, Tradeports > Refineries. Tradeports work pretty well anywhere, and more of them if placed strategically increases the income from all the ones you already have.

Refineries really only work well in specialized situations, that being several connected worlds with lots of resource nodes. In that situation they're great, but otherwise they're not that helpful. That just makes them more specialized, so you can go without them for longer.

Takes a good 3-4 planets to make trade ports worth the money. 2850 cred's for the first trade port (1500 for two civics, the 600 research and 750 for first port) to yeild an extra 1.2 creds a sec is steep.

I find upgrading your terrain homeworld to max pop yields an extra 2-3 creds a second for a cheaper credit price cost(the 225/225 metal and crystal are high tho). My initial build order is usually capital factory, crystal ex, 2 metal ex, 2 scouts, 1 colony, 1 akkon. By the time the akkon is built, i can buy 100 crystal and max the home population, and i know where i can explore and colonize. The asteroids usually have 2 ships guarding, so i send the akkon solo there, build that colony 1 pop slot and 1 emergency slot. Right about now your homeworld should be building its max pop and bringing its income from 10.1 to 13ish.

Somewhere after that i build 1 military and 2 civic research between home and the stroid. Any nearby asteroids i take the same way, otherwise i wait to build 4-5 cobalts to take any nearby ice/volc/terrain/desert planets. By the time you have the defense fleet moped, you should have your colonize for said planet researched, or trade ports if it is terrain/desert. As soon as the money is available, put trade ports on each of the 3-4 planets/stroids. Those trade ports should boost you another 5-7 credits a second, and you should be able to afford fleet upgrades/defenses and your whole grand strategy starts.