Official Answer received for Field Kitchen Support:
150 plus the crew of the Field Kitchen.
So if a Field Kitchen has a crew of 3, then each one can support a total of 153 people.
Now for a review of the debts, loans, and upgrades in BT books:
Interstellar Operations (2016 printing)
p345 - each turn is 4 weeks long
p348 - World Values Table Notes:
Upgrading a planet from a Regional Capital to a National Capital will pay for itself in 48 turns: 1920/(80-40)
Upgrading a planet from a basic world to a Regional Capital will pay for itself in 26 turns: 960/(40-2)
Upgrading a planet from a Minor Industrial World to a Major Industrial World (3+ factories - p347) will pay for itself in 60 turns: 960/(40-24)
Upgrading a planet from a basic world to a Minor Industrial World (1-2 factories - p347) will pay for itself in 27 turns: 576/(24-2)
If a world falls under two categories, it gets income for both (I.e. a National capital that is also a Major Industrial World will produce 120 RP/turn)
Observation: transforming a world into a Regional Capital that is also a Minor Industrial World will pay for itself in 25 turns: (960+576)/(64-2)
(This is ignoring the inherent bonuses to defensive troops that such an upgrade would also offer, based on p368 Garrisons)
p351 - Banking Resource Points. Non-spent Resource points earn 5% interest per turn (they are multiplied by 1.05). Since 1 turn is about 1 month, that is about 80% growth per year (1.05^12). It also means that banking RPs is economically better than upgrading a world to a higher category. This should be a concern for GMs as it encourages players to try to keep as much RPs in the bank instead of building up their planets (for others to blast into pieces). I propose reducing this multiplier to 1.005 (to be explained below under Campaign Operations Loan section)
Campaign Operations (2016-2021 copyright, corrected 2nd printing)
p31 - a unit's startup debt is paid off at a rate of 1% of the principal every month, with the full amount paid off after 150 payments (12.5 years). I don't have the math to calculate fractional loan amounts based on paying off a portion every month, so I took e^(LN(1.5)/150) = about 3.3% interest, and if it is compounded monthly this becomes .27% interest (or 1.0027 per month).
p50 - This is the loan table for various reputations. I'm sure there is a way to compare likelihood of surviving to pay back a loan with the loan rate (i.e. a bank might have multiple mercenary loans active that are all at 30% annual interest, but the rate of defaults might keep the overall investment package at ~5% interest).
My proposals:
1) Interstellar Operations: Banking Resource points needs to have its multiplier be reduced to 1.005, giving a result of about 6% increase annually. This also encourages the player to invest in their economy, instead of holding on to the RP. It also means the player has to choose between building up a world, or having the RP on hand to pay for emergency war funds.
2) Campaign Operations: Startup Debt is paid off at a rate of 2% the value per month, for 150 months. This gives an actual interest rate of 1.00735 per month, or 9.19% annually (just under the 10% annually for a merc unit with a Reputation of 1-4). Using 3% the base value for 150 months would translate to ~1.01 per month and 12.8% annually, and 4% the start value would be 1.2% per month and 15.4% annually (the minimum interest for a Mercenary unit with a Reputation of 0 or less)
Between these two values (~6% given to the ruler, and ~9% taken by the banks) is room for a banking system to function. Considering that mercenary units are putting their collateral on the line with every fight I am surprised banks will accept an interest rate as low as 9% annually. The loan table on page 50 shows that banks will demand a minimum of 10% for poor-rated units, so that does make sense.
(Next up, various building costs, construction costs, etc)