Training and ammo usage

From my experience, it doesn't matter how small your military is to prevent training expenditures. I thought the same thing you did and dismantled a number of military types in hopes of reducing the upkeep ammo expenditures. The number didn't even decrease. I imagine that there is a minimum number and I didn't have enough units to see anything higher, but it could just be a flat number or based on your population.

It's based on the number of that type of weapons your country has. It doesn't matter if they are deployed in units.

I wouldn't expect advantages for training anytime soon.

I've dismantled and sold everything I could in the past and I had no more ammo expenditures. I also only had to pay (what was it?) 3 billion per month to support the forts which I've never found a way to get rid of and some bases. Saved somewhere in the neighborhood of 7 to 10 billion dollars a month as a newer country. The fact that your country is in secure mode makes this fine unless you will be seeking level 2 or 3 for 100 gc each level increase. I've found increasing my level profitable so I would recommend building it up to qualify for level 2 and 3 (I forget what level 4 took, maybe more than one country). After you reach the level increase(s) and receive your gold coins put the entire military up for sale using [TRADE] > [WORLD MARKET TRADING] > [PRODUCTS IN STOCK: BUY & SELL]. You might as well hold on to all your ammo though, I don't think it costs you anything to stockpile it.

Oh yeah, and if you're interested in your score, selling off your military will make your war rank climb above 2000 which is going to hurt your world ranking. Pros & Cons, weigh them for yourself