my 2 cents: if money is not an issue, start off properly by leasing NATS for $150/mo, then changing billers in the future will a lot easier and you won't have to force your affiliates to change their link codes.

For billers, I would go with epoch and ccbill for cc processing and gxbill for phone billing. Both epoch and ccbill have their own strengths, if you want to maximize your sales you will research those strenghts and setup geotargeted cascades as appropriate.

cheers,
Luke