Untill the Zandor gives the low down...a squirrel fan is an extracter fan for sucking air out of the room,the light coolers should have their own fans built in..If you have a large reservoir the xtra pumps may be of a smaller 'power head' type to keep a mini wave system happening in the res which keeps the nutes well mixed or an O2 pump to keep the solution oxygenated[both optional] .EC and PPM are really the same thing...more important is a ph meter! dont overlook some insulation material to keep the feds from spotting your warm little grow yard![ I just insulated my mums whole house with this new thin NASA technology stuff...not fibre glass[which i removed and as a result i now have unlimited rockwool!]] What lights have you gone for?