Looking good!
Garden tests are a great idea but it's easy to forget the fact that the shower/ toilet is nearby as is the rubbish bin. A large pack of resealable wet wipes can be almost as good as a shower. Also, take some bin bags and leave some space in the pack to cart your rubbish out with you...
For water - I find that bladder systems like Camelbak, Platypus or MSR make for better packing - you can shape them to conform to available pack space and as they empty - so the bulk reduces, unlike solid bottles.
You'll find your own comfort tolerances with regards to sleep etc and they will be different depending on season - you may need a bigger pack for winter though...
Don't be tempted to fill your pack "because you can" - as a guide, my pack (about 60l) is about 2/3 full at this time of year even though it contains a lot of stuff like food - it's because I tend to stay out longer and have a lot of stuff to bring back (like mine and other people's rubbish!). In winter it's pretty much full of the extra comfort items like warm layers and I usually only do an overnighter - meaning less rubbish to bring back.
Oh! and don't forget spare batteries for your electrics and especially your mobile phone (your No1 survival tool) or at least a Powermonkey - or something similar.
Good luck and let us know how the experimentation went!