Q. Will I be able to access the server via FTP and via IP address prior to changing the nameservers ?

Ans :- Yes, you’ll be able to access the server through FTP or an IP address before changing the nameservers. And you’ll be able to preview your web site with a temporary URL.

[ http://ipaddress/~your username ] before changing your nameservers.

You can additionally load your web site, recode the pages for the new database and check it all before it goes live.