Just a few observations from playing SRCW.
1) Do not overheat your economy. Example: Build a bunch of factories (Industrial Goods, or IG, are the best, as they are needed for a lot of things) quickly, and you'll find you don't have enough Electric Power to keep them running. Build too many Electric Power plants, and you'll run out of IG. The key is to alternate building, a bit of each as needed.
2) Even rich countries can go broke. Don't try to build 100 IG factories on Day 1 as even the USA. It will break your economy. Slow and steady; this is a LONG game.
3) Higher levels of volitility (High and Very High) means a much more likely ahistorical world. At VH, expect (as the USA or USSR) to be fighting by mid-1951 against the other side. Fun, but only if you like a lot of conflict in the game.
4) A lot of conflict can either help or hinder game speed. The key point is what you (the player) does. The main problem with the overstacking issue is when a enemy country falls too fast and the AI has hundreds of units on the way to help. The first stacking issue you will hit will be Vietnam, then Korea. Ex: Player is USA. Korean War starts by event on 25 June 1950. Player takes out NKorea quickly (hint: use your dozens of paratrooper units but build the aircraft to carry them first!), but you have a long chain of Belgian, UK, French, etc allied units on the way to help. Once the target country (NKorea) falls, these units will not return home, but to the nearest friendly base. In other words, if you make allies with Spain before June 1950, they will come to help once the USA declares war on North Korea. If they don't reach Korea before the war ends, they will look for the nearest place to stop. I've ended up with dozens of Spanish units on Guam like that. The AI gets a bit confused and will take a while to 'unstack' and send units home--sometimes never. Hint: As the US, wait to make a bunch of alliances until you take out Korea (or as France player, North Vietnam). This does a LOT to reduce the chance of an overstack problem, at least until BattleGoat Games puts out the patch that will fix the issue.
5) Another way to limit overstacking issues is to kill a LOT of enemy units. Look for choke points (Turkey, Denmark) and send in subs and surface ships. The AI loves to move by sea.
6) Tech. The game isn't all that historically accurate when it comes to how fast you can get technology. Example: The US having F4 Phantom jets in 1953. Understand that the game isn't a grand geopolitical simulation, but a strategy wargame based on the awesome SR2020 series (and SR2010 before that). You can 'tech push' pretty easily by building a bunch of Research Centers. Don't feel too bad about 'gaming the AI.' Playing as the US, I've been surprised more than once by Soviet MiG-21's knocking down my F86 Sabre jets .
7) Development. Industrial Goods are key. If you are playing a big country (USA, UK, France, USSR) buy all you can at start, even if you go into debt for it. You'll need them--and use them to build up your own IG factories. By doing so, the AI will buy from you, and it will build more IG factories as well over time--you make money and help the AI run a more even game.
8) Social spending. Education and Health Care are critical to tech and pop growth, respectively. The most important is Infrastructure. The higher it is, the better supply flows, and higher supply means your factories, etc. work at a higher effiency rating. Ex: An IG factory running at full in a 50% supply area only produces 50% of its max. A 100% supply area, in other words, will produce twice what a 50% supply area factory will produce--effectively doubling your production.
9) Military spending. Look carefully at the unit stats. Some actually aren't as good in some ways as the units you already have. However, things like high stealth means your planes won't get shot down as often. Think about what kind of military you 1) want and 2) need. Only a few countries are so powerful that they can have everything on the menu; the rest have to pick and choose. Ex: South Africa is fun to play with US aircraft and Soviet tanks, mixed with UK surface ships and French subs, etc. If you are playing a major country, consider getting techs and building arms for "export." Ex: USA normally doesn't need the upgraded Sherman tanks techs if only building for itself. But what about getting the techs then building the Sherman upgrades for export? You can supply your allies with quality armor that, just in case they are defeated or have a coup, that you can beat with your top tech M48's, etc. Plus, you can make some real $$ on the deal...
10) Fun games. Want to have a wild game? VH Volitility, unclick Critical UN, set approval effects to Low, No Units start. For extra sexy crazy time, on Turn 1 (as US or USSR), break your diplomatic relations with everyone. The AI will go on a conquest game and the fun begins. One recent game saw West Germany owning everything from the Rhine to the USSR border by 1953.