You asked invision or phpBB , for your answer i would say Invision because invision has maximum security then phpBB , whereas Invision could not beat up vBulletin.If you have funds to buy vBulletin , then i would prefer vbulletin.
For the domain , I would say select a domain which people can remember + must be attractive.You could download a domain suggestion tool by doing a google search which might suggest some good domain names.
Cheers,
Muhammad Haris