Congrats! You are so right about making memories with your kids. My parents camped across country in a tent dragging 3 kids and sometimes a grandma. We upgraded to a pop up and did it a couple of more times as well as camped in parks through out Kentucky. Ohhh...the memories! Dad is gone now but I'm pretty sure he sits around the campfires with us when we're camping.
It sounds like you've got things pretty well under control and can fix most things (which is an essential skill when RVing!) Replacing the tires is so very important so it's good that you're getting that done before putting your family in it.
Are you planning on towing a 2nd vehicle? We did a year w/o a toad and while we managed, there were times when we really wished we had another vehicle. It's a real PITA to have to unhook and pack stuff away just to run to the store to get what you forgot....and we don't have skin-kids!
Grey water tanks fill quickly! Conserve...conserve...and CONSERVE. Black tanks usually fill a lot slower but with kids, you're still going to have to be careful. Remember water is the black tank's friend so you really shouldn't cut back on the amount of water used when the toilet is flushed. Sometimes, I use a dishpan to wash dishes in then dump the soapy water down the toilet.
What I would suggest before you take off for a weekend, is to camp in the RV in your drive. Pretend you're 3 hours away and see how you get along. Keep a list of how many times you have to go to the house to get something you forgot.
Have fun!