1. We started Tent Camping and cooking over an open fire, that migrated to Coleman propane stoves and griddles. That migrated to electric. So now, we use a flat electric griddle and an electric skillet. A lot of people will give you advise on their favorite grill. We discovered from cooking over a fire to using a propane grill, clean is no fun. When we switched to electric, it simplified greatly. I strongly suggest you carry an electric skillet AND a grill. You have options then.
2. At home, we've had Brighthouse (cable) and when we moved to the country we've had both DishTV and DirectTV. Both worked OK, except they continued to jack up the prices beyond reason. We finally canceled and use over-the-air only now. Either will work good for an RVer, BUT over-the-air is absolutely free! Consider your options.
3. If you don't have a tape measure, just use a piece of rope or string. stretch it from the ground to the highest point on the trailer. If the air conditioner is higher, add the distance to the string from the roof the trailer to the top of the air conditioner, then measure the string. I measured mine from the top of the radio antenna, which is the highest thing on the roof.
4.Never had a need for an alarm system. We've always been fortunate to park our camper at home. If you get an alarm system, it might be wasted money. By the time a storage facility reacts, or you are able to drive to a storage facility, your camper will be ransacked. A security system will require power, either battery or electric. Something else to consider.
As far as being out for the day? We've never had our camper messed with, but we always camp in State or Private Parks too. We don't boom-dock.
Ours is a travel trailer and not a 5er, but I DO keep a hitch lock on the camper 24x7. I have one, why not use it?