you can run from a home pc even whit 1 gb ram and 1.8ghz but... i recommend you to look for a server host company
whit 3 gb 2.5-3ghz and a 100mb line u pretty good whit l2j servers anyway normal max player for l2j is around 500~ because l2java lags alot whit alot players
l2joff i wouldnt even recommend it to start it on home server
6 gb ram 3 ghz dualcore 100mb line and its fine for the start. l2off files can hold whit the right hardware up to 4000+ players whit a minimum lag if its configured right