I know you've already chosen your server type but have you considered perhaps combining the two ideas? Some of the best servers I've played on were both gamemode and RP, separate locations for each.
RP servers:
1.) They are a big thing for a lot of Minecrafters out there, many just don't stay long because people make rubbish servers.
2.) If you want players to stay then make it worth their while - attractive structures, awesome mini-games, attention to what THEY want and kind, helpful, intelligent mods.
3.) There are a couple of things you need to get in order to ensure the safety of your server. Google will help. I recommend plugins that will back up your world every day and prevent grief.
xxx
Best of Luck!
