I did the numbers and got a very different result, I'm afraid. (And not one in our favor.) Here's my work. Please check and see if I've done anything wrong.
1.) A specialist or crafter is equal to 3 points of inhabitants (IPs)
2.) You need 2 servants for each 10 IPs (not including servants or teamsters), i.e., you need 20% of your IPs in servants. For 3 IPs that's 0.6 servants, who cost 1.2 IPs, since it's 2 IP/servant. That's a running total of 4.2 IPs.
3.) You need 1 teamster for each 10 IPs (not including teamsters), i.e., you need 10% of your IPs in teamsters. For 4.2 IPs, you need 0.42 teamsters, who cost 0.84 IPs, since it's 2 IP/teamster. That's a running total of 5.04 IPs.
4.) Each IP costs us 1 MP/year for basic costs (1.1 MP/year if we pay half-again wages). That's 5.04 MP/year normally, and 5.54 MP/year with half-again wages (rounding to 2 significant figures).
So by my calculations, I get that each specialist or crafter costs us approximately 5 MP/year, not 3.9 MP/year. Please tell me I've made an error in my calculations. I like your numbers better.
For reasons similar to those given above, I actually get 3.36 MP/year for each soldier, just counting the basics. Alas, that doesn't count the 1 MP/year in extra wages that an armsman gets. So that makes each armsman cost 4.36 MP/year by my calculations, or 4.86 MP/year if we pay half again wages.
FWIW, I get 3.36 MP/year for supporting a servant, teamster, or dependent, 8.4 MP/year for supporting a companion, and 16.8 MP/year for supporting a magus.
That also leads me to another discrepancy between our numbers - dependants. Now, I don't know how many dependants we're likely to have, but I think zero is too low a number. We're bound to have some children of the right age, idle spouses, infirm, or elderly who can't/don't work. And I'm afraid each one costs us 3.36 MP/year. Alas, there's no guidance as to how many dependents there should be. We'll just have to set a reasonable number.
In the end, my numbers aren't that much different than yours (assuming they're correct). But they do tend to inch up our expenses to the danger zone.
In fact, my bare minimum numbers (5 magi, 4 companions, 5 shield grogs, 16 servants, 12 teamsters, 0 dependents) is an even 136 MP/year. And that takes no account of labs, specialists, crafters, extra armsmen, tithes, extra wages, weapons & armor, or writing materials. Those can raise the numbers very quickly.