I assume you have an issue with your local network, likely your DNS and/or DHCP server isn’t properly configured and the problem is with resolving the hostname you use to access (BTW localhost cannot work for obvious reasons).
Read and follow the troubleshooting section/debug guide.
No it is not. And no you certainly won’t want to waste memory on a 3B which only has 1GB.
Would you please take care to read the docs more carefully before proceeding and asking here, plus provide the minimum requested information right away when you do.
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Yes in fact you can watch the install process on the standard web service port (80),
or SSH login as soon as possible, that’ll “auto-tail” the logfile while install is in progress.
It’s in the openHABian installation docs.