At first the idea of having such limited features as a free player turned me off, but if you say it's still able to be fun, I'll take your word for it. Since I'd be locked in, I have some questions:
A) Can you change your homeworld? If so, do we have some sort of B12 area going on?
B) If we're working together, what spheres are other people taking and what do we need? Alternatively, if we're not, what is in demand and reasonably fun to play/profitable?
I've been looking through the features, and the game seems designed to prevent groups of people from outside the game from joining up and ganging up on everyone else. I guess it makes sense. I know that the server is randomly assigned because of this, and to prevent general crowding on one server, and cannot be changed. As for changing the homeworld, I dunno.
Also, it doesn't seem like it's all that limited for free players. Someone already mentioned that on one server, one of the top 3 is free player. So far, it seems all you're limited from is just more than two spheres(also limited by your status anyway) to work with, but I think you can change your spheres. Looks to me that this is not pay2win.
I'll most likely pass on it, though. I think I lack the RP skills needed for it. If I do, though, I might take up the Psionics sphere. Profit from selling psychic services, plus espionage bonus.
In its favor, having extra spheres does not really matter, unless you are trying to be big like some of the more established or grow faster I guess. But you still need cash infusions from an older house... (to grow faster that is.)
Homeworld can be changed. Do not worry about that.
I and most veteran players recommend against taking Mercantile and Transport. Most if not all planetary random/negative effects really hurts Mercantile and Transport spheres... almost exclusively. It is a heck of a lot of work for not so great gain. If you insist on taking Mercantile, seriously, I insist you put money up for subscription, cause it opens up some ease of use features for that sphere. You will sorely need it.
'Coming in to conquer the universe' is not so easy here. You have many old established houses in each universe who may have an iron grip, both politically and militarily... and may be quite resistant to upstarts. Plus, it is going to take you real life months to be able to build up enough to even challenge the middle level houses.
The joining in one of the random universe is also something to prevent this.
Being profitable, depends really, spheres can be saturated on a per planet basis. You may find some other houses building the same type of facilities on your planets. There will come a point that it will cut into your profits. Even having multiple same buildings of your own, you will see yourself cutting into your own profits.
(This game does kinda suffer from the old houses owning many things and can make things move syndrome. Growth is at a snails pace without extra money from older houses. Though, it may in part also be because many spheres are also saturated/monopolized.)