You start up with an average income of $400 a day. You can buy resources, weapons and technologies from other countries.
Ok, the UN are willing to pay 100$ for every man you can send out to Berlin
7,000 Militant Militias.
Given that things like battlecruisers seem to cost a few thousand, I honestly cannot see any strategy better than investing what money we have in some minor gear and battle dress for our militias, and then renting them out to the UN. $100 for a five day tour * 7000 militia = $140,000 per day, or
350 times our taxation income. Drop taxes to 0 to keep our population happy, have the elites go around recruiting and training more batches to increase our income. The massive influx of troops will probably help them survive even if the UN doesn't provide equipment (and they would need to provide the uniforms at the very least), since people are much less likely to risk open combat against that many troops.
Eventually, we'll have to buy them all good equipment and actually do something, but I can't see a reason to irritate Ukraine until we
a) have beefed up our international standing by sending out all of these peacekeepers. Having international backing will definitely help whatever we end up getting into with Ukraine.
b) have gotten our troops a bit of training, gotten them into a command structure, picked out some for more training, etc. Ukraine has a military two orders of magnitude larger than us, plus air and naval power. If we go against them right now the best we can hope for is a long drawn out guerrilla war, except that we don't have fanatics, giant arms caches, or a friendly backing superpower, and so we'd just get ground down.
c) made enough money to buy whatever it is that we want, rather than scrounging around for a few M16s. If a used Kirov is $2200 with shipping, we should be able to have the equivalent of the Pacific fleet, and all of the latest everything for all of our soldiers, in a few days.
If someone (like Ukraine) starts trying to bother us before we're ready, we can pull the "we're just an innocent ex-soviet country trying to take our place on the world stage" card, which should have at least some backing because of the work that we're doing with the UN (and Russia apparently likes us). Yet another reason not to do anything aggressive too early.
Upgrade the infrastructure, too. It's great that we can buy M16s from Russia and all, but I'd much rather if we had our own factories etc. producing our guns. Producing our own T-72's, or variants thereof, would be great. Plus, jobs (even factory jobs) make people happy.
Now then, once we're rolling in money and guns, we can start thinking about taking territory. We can reassure our populace that it will be in two weeks or so, and meanwhile they aren't being taxed.
When the fighting starts, taking naval and air superiority is going to be important, but hopefully we'll be helped there with top of the line equipment, the support of the international community, and the support of the Ukranian people when they hear that we won't be taxing them either because we'll just require two years military service or something and that will raise more money than a lifetime of taxes. The goal will be to take some territory and make it too economically and politically costly for Ukraine to take it back, rather than going for open war. A more espionage-based war might work too, but let's see what our options are before getting ourselves squished like the bugs we (currently) are.