We purchased a modular home in 2008. At the home inspection, the inspector found the 100 amp meter breaker box on the pole had some issues. The sellers paid to replace it, and we gave the electrician additional money to upgrade it to 200 amps. This 200 amp panel has the meter with 20 spaces and a 200 amp main breaker attached to a utility pole, "we own". Inside this 200 amp panel is;

A 100 amp breaker that feeds a 100 amp panel in the home using #4 copper in 1 1/2" conduit. Factory installed in home.

A 60 amp breaker that feeds a sub panel in the detached garage 55' away, #4 copper wire in underground conduit. The sub panel is 6 breakers main lug. We only use 2 breakers, one for 1/2hp door opener and lights, and one for a couple plugs.

Lastly, a 30 amp 220 breaker for a well pump. The city put in water in 2010, so we only use well for washing car and garden.

Inside the home, we have electric water tank, stove, dryer, washer, microwave, dishwasher, fridge, freezer. My wife has asthma and we want to install a 15,000btu ac unit in the window this summer. I will run a seperate line for it, "120 volt and requires 20 amp breaker."

We currently experience no breaker tripping issues of any kind. I realize adding the AC to a 100 amp service already loaded up may cause issues.

What I would like to do is this. Add a sub panel in the utility room near the 100 amp currently there. I have #4 copper cable "got it free", to run from this panel out to the 200 amp main panel on the pole. I would put it in 1 1/2" conduit. I will feed this panel with a 70 amp breaker from the 200 amp panel. I want to put the stove, washer, dryer, and ac unit feed into this 8 space main lug sub panel. That will give the 100 amp house panel some relief.

We originally wanted the house panel upgraded to 200 amp, but they wanted it on the pole ? That would have eliminated this. I guess because it's a modular.

The 200 amp box on the pole will then have in it;
100 amp breaker feeding house panel that has it's own 100 amp main also.
70 amp breaker feeding house sub panel
60 amp breaker feeding garage sub panel
30 amp breaker feeding well.
I did the usage calculation thing, and we would never use anywhere near the amps or watts.
Is adding this 70 amp sub panel legal??

I've been told by my local electrical inspector that I can have a maximum of 5 sub-panels (assuming they are done and sized properly). Adding a panel should require a permit, and a resulting inspection. Ask the powers to be if it is okay. It could be a pain to run a new larger feed to your home and increase your factory panel capacity to 200 amps; but you're already going through the trouble of adding another.

I've been told by my local electrical inspector that I can have a maximum of 5 sub-panelsIs this something you let him dictate, or do you know this is a code requirement? I've never heard this one before.
I have commercial customers that have a dozen or more subs all over the place.

Is adding this 70 amp sub panel legal?? In your case you cannot have more than one feed from the pole to the house. You are only allowed one feeder to a detached structure, which is what the house is considered from the pole. You could ask an inspector if he would allow it, but according to the letter of the NEC it is not allowed.