Just tried playing as the Romulans. Two things I noted:

1) The Romulan planets all start off with the new colony capital building. I think Romulus and Remus at least should be the planetary administration.

2) Starting populations on these worlds seem a bit low. With the new economy I find it's really important to grow planets slowly, maybe when you have about 200-300 jobs available maximum. I think all these planets start with about 800+ available jobs.

3) The economy of Romulus almost immediately crashes in terms of mineral production meaning you have to manage it all very carefully, but given your planets have such low pops etc it takes a lot of work.

4) Amenities seem almost impossible to produce. A few buildings say "produces amenities" but they produce so little pretty much every planet was running at a deficit of -1,500 amenities even early in the game even with a commercial zone and a holo theatre. Even if the national monument worked (see below) requiring 2 buildings to produce amenities to meet the minimums is just too much building space for every colony to require.

5) Dilithium mines are limited to the specialisation of the mining district only, but this means it can be quite a while until you can start mining dilithium as you can't build it in the city district.

6) The national monument building doesn't actually produce anything, as such pops don't work it.

7) I think for a nation/empire like the Romulans you very quickly find yourself unable to field enough fleets to defend yourself. The game ran ended as I was invaded by two coalitions, neither which with a total fleet strength greater than my naval capacity, but I was running a -100 energy deficit with less than half of my naval cap used.