Adware > none
Virus > Virtually None.
ISP > Any really, i guess, dependant on your hardware.
Hi spec machine, goes anything up over £500 for something like an A4000T (C)
To be honest, Id rather go down the AmigaOne route. But if your wanting classic C= hardware, dont expect to get 2005 style webpages on a 1992 machine. Its not going to happen (at least not in the way you would like).
Best to speak to someone like RyuMiggy, in the #amiga.org chatroom. Im sure he would be happy to advise you (he uses an Amiga 1200 / BPPC for his internet connection).