There are trip logs on the adventures.com site for both the trips you mention. And, on the pci map on that website you can see the pics people have taken of some sites on the lakes you mention. That maybe a help  if you didn’t already know about it. As far as the smoke lake and onward trip, my daughter and I did smoke to ragged to bonnechere, Phipps and kirkwood in September of last year. Ragged was very very busy with firewood very hard to come by, at least on the site we were on for the night. Porcupine was nice but we didn’t camp there,bonnechere had 2 sites we liked, the famous ‘gaga’ Site ( pci map #2)high on the rocks which was occupied, and the site we ended up on which is between cradle lake and bonnechere. ( pci map#6) The other sides were not so much to our liking, some small, some uneven, some deep in the trees, but everyone has different ideas on what they like best. The paddle through porcupine and bonnechere and on we found very scenic, especially Phipps and kirkwood. The channel connecting bonnechere and Phipps had high enough water to paddle last year, but others have said it can be quite low. The first site on phipps was reasonably flat with about 2-3 tent spots if they’re not too big, we passed the next site due to a steep incline. Kirkwood island site was very sloped, with only one flat tent spot on top. Pics on pci map.
As we did not make it a loop I can’t help you past kirkwood. We paddled back and spend time on park side bay, off of ragged, which had wonderful sites on points etc. These sites were quite large.
All in all we loved our trip, but there were definitely people around,although I can’t say it was busy once we entered porcupine.
Hope it helps.

Another option for you is Rain- McCraney, and across to Hot, Wee, Weed, Way. and Islet, back out to Rain, There is one long portage+- 1800M, but it's literally as flat as a board (old railway bed) and, if you want, there are jump off sites near the dock at Rain.

You're going at the busiest time of the camping season, and don't have much time or the inclination to travel far, so don't expect a serene wilderness experience: you're going to have company wherever you go. But I'd say your Rain Lake access point plan is as good an idea as any, given the restrictions you're working under. 

Avoiding Hwy 60 in mid-August is always a good idea!

Yes, I should have added that while I haven't been on the Little Misty site,  I've paddled closely past it (and seen it in a number of trip reports) and it doesn't look terribly exciting. Little Misty is really just a slight widening of the Petawawa and isn't much of a 'lake'. Spend your night on Misty instead, which is beautiful lake with a number of good to great campsite choices - you'll be happier for doing so. 

I've done the Rain Lake trip you've described, but in a slightly more efficient way.

Day 1 paddle into Moccasin or Bandit, Day 2 paddle the Petawawa Loop into Misty, Muslim, Wenona, etc., Day 3 out. You get to see all the same stuff, but you're only building camp once.

Also, I've stayed on Little Misty on another trip and loved it! Fair amount of traffic will go past you, but once the evening arrives you've got your own lake.