IME, as long as Annabelle is planted where she gets sufficient moisture and morning sun or really bright shade, you couldn't beat her back with a stick. Pretty much any size will grow well, since I've rather rudely ripped out chunks of mine to give to friends, and they have all thrived. I would be surprised if you can't find Annabelle locally.

Just so you know, Annabelle suckers (which is why I find myself ripping out chunks) and it's easiest to keep under control if you remove suckers annually. You should leave at least a bit of room between the building and the size you want the plant so moisture isn't held against the building and also enough room between your hosta and Annabelle to remove suckers without disturbing the hosta. My Annabelle got really out of control when I had some knee problems and this is how she looked before I got her managed again. The bed is 12' deep, and Annabelle filled more than 10' of that, and was as wide as possible between the two adjoining shrubs. She was sending shoots under the poor spirea.

So that is perhaps a long way to say that I'd give Annabelle at least 4'-5', but you can give her more than that, and you really do want to keep on top of the suckering. I had to work much harder to remove older suckers than newer ones.

" I don't need access behind them."

Yes, you do. You want rainfall to actually reach the plants and a building blocks that whether it has eves or not. You want light and air to circulate freely. You want to be able to walk and trim if necessary. You don't want to provide a haven for pests right up against your house. Someday, believe it or not, you will want to be able to access the structure itself for one reason or another. And finally- aesthetically, nothing looks worse than a row of plants crammed up against a building. They need room to sprawl and make the house look nestled in, not artificially plopped down.

Be smart and leave room at the back.

Ditto that. Especially if you have pin-holes in blocks and trim. For example, I've battled many-an-army of little black ants trying to get into the house. They leave no surface of travel unturned and the fewer bridges they have to your dwelling, the better of you'll be.