blown in cellulose tips / tricks

I decided I really need to do something about my insulation. I want to do the blown in cellulose from home depot. If i buy 10 bags i get the machine for free. Next weekend I'm going to be attempting this and i've never done it before, however i'm really handy. I've gutted rooms, redesigned them and rebuilt them in the past. Are there any tips or tricks from some experienced people on making this work?
Im going to do my dining room first, since well it will be a test room. It's already closed off for the winter and easy to keep the dust contained and gain some experience.
I have some questions -
Will 10 bags of this stuff fit in 2 normal sedans or should i borrow my friends e350 van to get it home?

Will the machine fit in a normal sized sedan (subaru legacy)

I want to pre drill the holes before i rent the machine. how big should my hole saw be? online i saw people recommend everything from 1" to 3" inches with 1.5 inches seeming to be the most recommended.

Also there are existing batts in the wall. I know for a fact these are in horrible shape and doing absolutely nothing insulation wise. Can this project be completed with those batts there? will the hose be stopped trying to get through it? I know from a previous wall repair the batts are like swiss cheese now.

I plan on doing the attic soon as well. First the dining room this weekend, then the rest of the house, then the attic. I will have to hire help for the attic, at least to staple in the soffitt baffles, as im getting kind of old for that.

Thanks for any help.

Ok gave it some careful thought after reading all the great feedback here. I gather i'm not to expect perfect results - and thats ok with me. I'm not looking to heat my house on 1 ton of pellets a year. I just want the house to retain heat a little better than it does now without a giant expense. I think i can meet those expectations doing it myself. I decided I am going to just do 1 room (the worst room draft and temperature wise) which is my dining room. I'll see if it makes a difference or not. currently we close this room off for the winter because it is so cold in there. We just use our eat in kitchen. If it doesnt seem to have helped at all, then i'll give up and hire a pro for the rest of the house. For the money and the weekend spent it is at least worth a shot.

I will however do the attic in the fall. I know a lot of heat leaks out that way too. If all this just gives me a moderate result i'd be happy. I'll let you know how it went after the weekend. I already have new windows in the room in question, and 1 of the 2 outside doors will need to be replaced. the other one is good. I'll be doing that too. lot of work this weekend. I put the holes in tonight after going to the box store to check out the machine. went well. not much wiring at all in there. The dining room used to be a garage and it was finished into a dining room by the people before me. they then built a 2 car separate garage on the other side of the house. I think this explains why the insulation is especially poor in there. A neighbor had told me it used to be a garage. I had no idea. I then went in the crawlspace and saw the old garage concrete slab still there, and the oil spot where the used to park the car!.

Well the project is done! It went pretty smooth, although i was covered in insulation. luckily it was the no itch stuff. I had a cartridge style respirator which i liked a whole lot better than the masks. Few surprises. I drilled the holes, and found most of the insulation was gone? The paper was still there, just no insulation attached to it. I was able to pull the paper out through the holes which was loose and crumbled in the cavity anyway. I do know this place had a mouse problem with the previous owner. It was the first thing i took care of when i bought it. Maybe the mice stole it? I have an inspection camera and took a peek in some of the bays. all clean of insulation. Not having the batts in place made it fairly easy. The machine never clogged on me, although my helper (wife, who btw im still shocked she agreed to do this) complained that the hopper paddles didnt always start up when she turned on the machine.
I cant tell if there is any decent results tonight. the stove is working overtime as i had everything opened up all day to keep good ventilation.

I would definitely air seal the attic first, i can do that with a few cans of foam. Then i would just hire help to staple in baffle vents and blow over the old attic insulation. Im guessing the attic would provide a good bang for your buck vs doing the walls in the rest of the house. the current plan is dining room, attic then wait a winter and see if anything else is needed.

Thanks for the advice. Much appreciated.