Okay first a disclaimer: I am a Trotskyist albeit one who is not involved in Party politics anymore (so not much of one basically, a bit like being Catholic but not going to church) so if that makes me too biased in this situation for you to pay attention to what I have to say I'm not wasting your time. Saying that I don't think that Trotsky did everything right and I agree that at times he could be a ruthless git.
Okay on Communism, to my mind there has never been a communist state, there have been plenty that call themselves communist but then their are plenty that call themselves democratic and aren't either. Communism is supposed to be a world without a state, basically the idea is that first you have socialism and then over time as people get used to organizing things themselves the stat is supposed to wither away as it basically isn't needed anymore. Personally I'm not sure this could actually happen totally (maybe in a post scarcity world but that's not likely to happen soon) but think that the journey towards it would be beneficial even if we don't get there. There have been socialist states, but my argument is that they have all failed to remain so. This leaves us with what to call the USSR and other similar states which I will address later.
There are a number of differences between Trotsky and Stalin, first there is their background. Stalin was a terrorist who spent his formative years in Georgia mostly training to be a priest and had a fairly brutal childhood. Trotsky was Jewish and was sent to Odessa for his education, later acting as a trade union organizer only gradually sliding into being a revolutionary socialist. This to me speaks of what they were to become. Trotsky an intellectual internationalist, Stalin a brutal enforcer of doctrine (albeit a changing doctrine of his own design).
Basically what happened was during the civil war the Bolshevik government was having a lot of problems, they controlled a lot of the country but not all of it, the country was run down by war and the revolutions that had resulted from it, the revolutions that had sprung up across Europe had failed leaving them isolated and fighting a war on multiple fronts against pretty much everyone. This resulted in a policy known as "War Communism" which basically was "do what you must to keep us from losing" followed by NEP (New Ecconomic Policy) which can be summed up as "yay we won the war but everything is broken and we need to rebuild so we'll loosen up a bit". As the revolutions had failed abroad an ideology grew up of "Communism in One State" basically that Russia would have to go it alone being as self sufficient as possible but also dealing with capitalist countries, Stalin championed this ideology. Trotsky on the other hand championed the idea of internationalism, that the revolution must spread or die and that cutting deals with the ruling classes of capitalist nations doesn't help the workers who we want to have a revolution.
I would argue that Trotsky was correct because following Stalin gaining control of the Soviet Union the remaining elements of socialism were gradually stamped out. This brings me to what I would call the USSR (definitly from Stalin in charge onwards) which is State Capitalist, basically the state owns everything and runs everything for the benefit of the state (or more accurately for the benefit of those running the state). Basically from this point on what is happening is that the USSR is gaining control of other countries through force more then through spreading ideology (basically do what we say, follow our doctrine (at least lipservice) or its tanks on streets time). Basically "Communist" countries other then the USSR can be grouped into 3 groups, first group are your countries that came to "Communism" under their own steam and were too strong for the USSR to just do over (the PRC and Yugoslavia (Yugoslavia particularly just after the war which was significant)), the second group are countries that are easily accessable enough for the USSR to send the troops in (like the European Eastern Block nations), or thirdly nations that are far away and who hate the other side which are the ones that are freeist in their own actions (Vietnam, Cuba, Angola and so on).
I would have two mutually exclusive chains of National Focuses, one for a Stalinist one nation policy and one for a Trotskyist internationalist policy. Basically the Stalinist chain would be a series of purges (increasing national unity and maybe like the equivelent of Party Org? but harming specific areas, so purge the armed forces (damaging the org of the armed forces, maybe loose some officers/manpower), purge the academia (damage research rates), and so on) and industrial/law reforms to make the USSR more powerful militarily. For the Trotskyist one I'd say have the initial ones be disadvantageous (say like first have "Encourage Debate" or something which reduces national unity, military org and industrial efficiency but increases research rate and PP gain?), some which increase the likelyhood of socialists taking over countries (civil wars and so on) and maybe makes your own troops you send as volunteers not have the org problem or have something that cancels it out (a "Spreading the revolution" positive bonus for troops fighting as volunteers for socialist factions in civil wars?) and later on ones which basically take away the bad parts of the earlier ones and increase national unity beyond what was taken away.
Basically it would be a choice between a militarily strong and unified USSR but with few friends and a little bit backwards to a militarily weak (in numbers at least) but advanced USSR with lots of friends. To me this would make it a real choice and add a lot to playing as the USSR.