hmmm, twice the size of the ram is on the lower side... I'd be more confident with a 3:1 ratio, otherwise you will have a large pressure drop. Maybe someone else can confirm this. Btw, the difference between a 12 and a 9 oz bottle is not that much, the 9 oz bottle measures 26cm by 5.5cm dia. the 12 oz is 26cm by 8cm dia. Regarding plumbing, if you select your components wisely you can fit the whole system in a very tight space and keep weight to a minimum.
Just as an example in my first version of my robot I used 1/2" fittings and valves throughout, need less to say the system was heavy and quite large. The new redesigned system uses mainly 1/8" fittings and valves and only where necessary did I use 1/2" parts. This way I'm to loose about 1.3kg off the pneumatic system!