Hi and welcome to the forum
Sounds like a great group, and having the minibus makes everything much easier! The south side of Loch Tay has a perfectly good road running its entire length (unsuitable for towing caravans, but fine for a minibus) so you could consider spending two nights at either Lochearnhead or Aberfeldy, whichever gives you the best deal for accommodation to suit your group. That also has the advantage that you avoid a round of packing and unpacking and finding out where B&Bs are. Personally I'd go for Aberfeldy if you can find what you need there, it has more diversity and facilities.
The B&B at Acharn is too small for your group and the one in Ardtalnaig (01567 820771) is well past the halfway point, but worth a mention because unsupported walkers might use it (especially if they start from Killin rather than Lochearnhead). I don't know about its size or facilities. Has anybody tried it?
I'm not sure if the minibus should go beyond the car park at the eastern end of Loch Venachar (shown enlarged on our page 41 clip map) but can't see why you would want to as the East Lodge is only 5 minutes walk beyond where the Way comes off the hillside and forest road for which you need permission: or have I misunderstood? But if you want to reduce the length, and arguably improve the quality, of day 1, why not consider starting your walk at Drymen Road Cottage and making it a glorious 16 miles of off-road walking? This is where the Rob Roy Challenge starts, a major event that runs each June:
http://www.robroychallenge.com/. This avoids a 3-4 mile slog along minor road north of Drymen and keeps time on your side. (There should be up to 18 hours of daylight even in early June, but I'm factoring in travel time to Drymen.)
Whatever you decide, do let us know, and enjoy the Way!