It will be interresting to see how the encapsulation of these chips are, some say the QFN are plastic, that would be interresting with hot-air?
I gues using 0402, 0603, 0805 doesnt make too much difference to the design, other than the bigger, the easier for the DIY'er?
If you go that route, stencils + pcb's, that's very interresting, but, could you adopt the stencil8 system?
http://www.hoektronics.com/2012/10/27/super-simple-smt-stencil8/https://www.tindie.com/products/arachnidlabs/pcb-fixture-block-for-solder-paste-stencilling/supereasy system for DIY usage, only needs 2.5mm holes, on an 10mm grid at clever places.
Pretty much all electronics parts now are designed to withstand reflow oven processes. So even if they say "plastic" it's plastic that can take the heat, at least for a suitable period. If you blow hot air on it for too long you'll toast it so caution is required.
Smaller is harder but I'm not sure it matters. One of those magnifying circular light dealies is recommended.
Parts count is the killer. I just finished the prelim parts list and pushed it to github. There's 320 parts on that 10x10cm board. Ouch!
(Someone please send me a Pick n Place machine)
That's a sweet looking registration rig and oven at hoektronics but I'll just be using the Sparkfun method - tape some boards to the table and tape the stencil to the boards. Oh, and a toaster oven.