This is a little long, but with your situation and being new to the motorhome, these thoughts may be useful.
The two of us had no problem staying cool in west Texas driving all day in 104 degrees with only the cab air conditioning. The relative humidity was 4% and there was a 20 mph wind. It was probably in the high 80's in the coach when we stopped for the night so I set up a fan to blow air on us while the A/C cooled the coach. It took several hours for the A/C to cool it down to the low 70's. If you are in 100 degree Florida humidity the coach A/C won't cool as well as it did for us in dry Texas because some of the A/C output is being used to remove humidity. You may need to run the generator and coach A/C because when you stop for the day it would take a longer for the coach to cool down. The generator uses between 0.5 and 0.7 gallons per hour of gasoline when it is running loaded.
To cool the coach down faster, you can open the downblast vent on the A/C unit, close the ceiling vents in the rear of the coach including the bathroom, and close the door to the rear. This puts more air into the living room area so it will cool faster. Just open up the rear area after the front has cooled off.
Would you be in difficulties if you had no shore power and the generator failed or didn’t start? You may still want to consider an good inverter so you can run your equipment off the coach batteries in case the generator fails. (You’ll have to get someone else to tell you what inverter to get so it doesn’t harm your equipment.) I believe the Onan is quite reliable, but things happen. The coach’s automatic transfer switch could fail. You could get some bad gasoline, etc., or the gasoline could go bad during storage. Small engines don’t tolerate bad gas as well as automotive engines. If the coach batteries are low you can run the chassis engine for 12 volt power. The coach’s battery control center will connect the chassis 12-volt system to the coach’s 12-volt system so the chassis’s alternator will provide 12 volts to the inverter. (On the other hand, if you are in a campground I have no doubt that you could get someone else with a generator to supply power to you.)
Here’s another tip about the generator. The generator is normally started by the coach batteries. If the coach batteries are too low, you can’t start the generator with them, but if you start the chassis engine, the battery control center will connect the 12 volt systems and the generator can be started. You can stop the chassis engine as soon as the generator is running.
Also, be sure the dealer gives you a thorough check-out on the coach’s electrical systems. You need to know where the coach’s 120 volt circuit breakers are, which receptacles are on which breakers, and especially where to find and reset the generator’s built-in circuit breaker. You may trip a breaker if you are running your equipment and another heavy load like a space heater is on the same circuit. There is a GFI receptacle in the bathroom that feeds other receptacles. If the GFI is tripped there will be no power at those other receptacles. The GFI can be tripped by accidentally pushing the test button and you will have no power even though the breaker in the coach’s panel is still on.
If you have a problem during a trip and have a laptop or smart phone, you can post a message to this forum. If you title the message with something like “Help – on the Road” you may get a reply pretty quickly.