For the 48 gallon, you would need three additional 2L bottles and the appropriate number of airline T's.
The bubble counter is nice but not strictly necessary. One thing that is a good idea, especially if you're using a yeast that likes to float (like Fleichman's) and/or your bottles are likely to get bumped is a gas separator. This also serves the purpose of a bubble counter, but more importantly will keep the yeast mixture from making it into your aquarium. Not sure of the size of the bubble counter that you linked, but the basic setup would be the same. You'd want at least a 1L bottle for this.
With as large of an aquarium as you've switched to, it's going to be much harder maintaining good CO2 levels. This means that you'll want to use an extremely efficient CO2 diffusion method to make things easier on yourself. Neither of the diffusers you linked would fit the bill. You could use one like you described building (plastic mesh kitchen scrubbers would work better than the poly fiber), an Inline CO2 Reactor (which can be built with PVC), or the mist method.
The bubble counter is nice but not strictly necessary. One thing that is a good idea, especially if you're using a yeast that likes to float (like Fleichman's) and/or your bottles are likely to get bumped is a gas separator. This also serves the purpose of a bubble counter, but more importantly will keep the yeast mixture from making it into your aquarium. Not sure of the size of the bubble counter that you linked, but the basic setup would be the same. You'd want at least a 1L bottle for this.
With as large of an aquarium as you've switched to, it's going to be much harder maintaining good CO2 levels. This means that you'll want to use an extremely efficient CO2 diffusion method to make things easier on yourself. Neither of the diffusers you linked would fit the bill. You could use one like you described building (plastic mesh kitchen scrubbers would work better than the poly fiber), an Inline CO2 Reactor (which can be built with PVC), or the mist method.