Thanks for contacting us. To answer your questions, yes you can use High Purity N2 in place of Ar as long as it's from a liquid source (blow off from a dewar or liquid tank).
If you're all set with that then we could fit a five solvent system inside 43", I attached a drawing for you to look at. As for ventilation that's your choice, most just place the system in the lab, others do more. It's really a case by case basis depending on EH&S requirements. If that all looks good, let me know which solvents you want in the system and I can send a quote over. - Thanks, Pete Sampson, PPT President