Personally I recommend 7.5.5. 7.6 was the first release that cost so 7.5.5 was the last free MacOS. Also, IMHO 7.6 introduced several bug that don't appear in 7.5.5. You need to download and install the 7.5.3 system, then update to 7.5.5, and if you want internet access, you also need to install Open transport and opentransport PPP (for dialup).