As a reasoning for my first map, I did not used the morals of present day and I am not encouraging any claims on the today borders.
1. I think Transilvania, Crisana(Trianon), Maramures Ugocsa Bucovina and Banat(Trianon+ a portion of plain linking the Danube) should be viewed as cores in the first step and should be taken with the possibility to develop them. So Banat should have plain acces to Danube, Maramures should have the rail link and the mountains to protect Transylvania.
2. Pocutia, East Transylvania and Timoc should be considered as a next step, since they control vital routes that link Oltenia to Banat, Maramures to Bucovina and Moldova to the rest of Transylvania. So this would be a gain to consolidate the proper cores. Of course, most likely East Transylvania will be included in the the first step in any realistic scenario, but I took into account all possibilities.
Minorities would have the rights and they had/have a similar culture and way of life with the majority, being mountain peoples too.
3. Now, concerning the east, I took in consideration the power of Russia and the alliance system. A direct confrontation should be avoided and only if the politics allow it, a union/annexation should be considered. Taking a part of Transnistria would make the defense of the Dniester more easy and will give full control of the river so will enhance the economy of Moldova as a whole. This could be the first step as it happened in reality, but that would be the reasonable tactic since they were controlled by a superpower.
4. Bulgaria should be an important allied and Romania should take lands in Dobrogea just to secure the link with the sea for Muntenia, by Constanta harbor. South of this line the land should be used as a tool to get a part of the Bulgarian Timoc. Any claims beyond the 1900 border should be viewed as a madness since Bulgaria has a long border with Romania and Romania needs an allied, also the cultures are close. I think that was a mistake on Romania's behalf to annex Cadrilater.
5. Serbia should not be made into an huge enemy, but the relation should be as normal as possible, so west of Banat should be claimed only if Timoc lower valley is not part of Romania, as a negotiation tool. Should be pursued only in an extreme scenario, let's say, Hungary/Germany/Austria would conquer Serbia.
Maybe Serbia will not make a life or death situation from a minor loss in Timoc.
6. Rutenia, the rest, should be given to Hungary or Slovakia with an emphasis on minority rights as a negotiation tool. Should be pursued only if the rest of the solutions will not benefit Romania by that time and the population wants to enter Romania.
7. South Transnistria should be viewed as a buffer and the Ucrainian population should be encouraged to form a state. Should be pursued only if they want to enter Romania as a protection from a future annexation from Russia.
All lands who are not vital to the security of Romania, in Hungary, west of the Trianon line, should be a big no-no and should be left a part of Hungary regardless of the scenario, because even by those standards that will be a very imoral solution and blatant Imperialism from a very young country to take them.
I also took in the consideration the unlikely succes of an Ukrainian state in that period, with Poland, Hungary, Slovakia and Russia as enemies. So spending efort on helping Ukraine and leaving Pocutia or parts of Maramures- Bucovina for them will not be realistic. Also the population has some ties as culture and vocabulary with the Romanian one and could be integrated with fewer efforts than the Hungarian one. Poland will not mind that Pocutia is in Romania, they would have other problems.
Some scientists claim that Hutuls have a Dacian or Romanian substratum.
As for Aromanians that will complicate the scenario too much and will make Romania vulnerable on her southern borders, I will fallow the same policies of educational help, but not political help.
Also, Romania taking lands that were subjected, I think the population will not agree with colonies and will go against the culture of Romanians. So for me is a big no.
I hope nobody will be offended and view this as a way to encourage Romanian iredentism. That's not the case.