Not much around Aviemore itself.Couple of suggestions would be,dependent on time of day you could get the bus from the centre of Aviemore up to loch Morlich and walk up towards Ryvoan where there are wild camping spots as you exit the forested area or walk up to Coylumbridge and take the Lairig track towards Piccadilly.On that path there are a few low level riverside spots.Alternatively off that same path there is a fork for Loch Einich which if you want to walk about 8/9 miles you will find seclusion.
Walked through last year when I walked from Strathcarron to Fort wiliam
If you do intend to camp near A,Chuil bothy walk on about 1/2 mile from the bothy,there,s a decent bit of camping ground on a river bend that I used last may. The numbers might be a problem. Theres not much decent ground around the Bothy itself
In relation to the track from Sourlies to Barrisdale I did it the other way with a full pack in 6 1/2 hours so it can be done.
If you are unfamilar with the area there is a bit of route finding to get from the path from about grid ref 897002 to the Mam Unndulain track where the path stops and you have to clamber up a grassy spur.
In relation to the midges they wil ruin it,I dont suppose you could change to May?
If you are up there in the winter have a trip up Hedgehope hill (heejup). The view from there on a clear freezing winters day is awesome. Right into Scotland,to the northumbrian coast and right down to Tyneside.
For my money in the right conditions the best hill in the Cheviots.
I was last up there two winters ago and actually had to turn back as the snow was about 3 feet deep and too soft to walk in!