"Where is the portage into Baptism proper anyway? Right? Left?"

its "river right" - I think all the portages along Baptism Cr are on the right.

As said above by others, it is hard to see/find the entrance to Baptism Creek - in fact, it is hard to see the entrance to French River out of French Lake - people have missed that and gone paddling the Pickeral River and on into Pickeral Lake. (if you are on a fairly wide section of "river", and the bent grass is showing the current moving with you, that is Pickeral River).  I've only gone up the French River in end of May first week of June timeframe - the current was very strong then, about all we could handle in a tandem. Should be considerable less in August.

You can't see the French River - it enters the lake in a back bay, so just stay along the left shoreline to find it.  

Its easy to miss the entry into Baptism Creek because you'd have to be looking back over your right shoulder to see it - as you are going up the French River, you will pass under TWO bridges (I assume the second one is still there - my Fisher map only shows one bridge, but there were two several year's ago.)  About a hundred yards or so after passing the second bridge, there is a small backset to your right where Baptism Cr comes in - you have to be looking for it, as it isn't obvious.

One of the portages after you leave Baptism Creek was changed by a Beaver Dam - it broke up the portage (the longer, second one I think?) into two distinct pieces - seperated by the new beaver pond - we paddled thru the pond, but it was full of floating logs and not the easiest paddle - just went straight across to find the continuation of the trial.  That would be a good question to ask the rangers, i.e. when those portages last had maintenance work, and if the portage has been re-routed.  In any case, that portage did not match to the map either.

The rangers will advise you about water levels - if its low, they will tell you Cache River is "too low" - not sure how accurate that will be, but with low water, it will be a really really long day to do the whole river.
Even in early June, most of the river is stillwater - no noticeable current, but most likely strong upstream winds - that's been my experience.

Essentially, there are no campsites along the river - it is bog lined almost the entire way unitl you get close to Kawnipi (the last couple of miles or so).  There is one area at the downstream end of one of the portages that had a fire ring, that would be a doable campsite that I recall - there might be one or two more similar spots ot other portages. There are one or two big rock outcrops that could be used in an emergency if you have a free standing tent (I've never checked them out, just noted them in passing) - they are about 2/3 of the way down from Cache Lake as I recall, but don't bet money on that location.  

I'd just plan on a first-light start from Cache Lake, and plan on making it to Kawnipi in one long 12-14 hour push.  In August, you will have more portages than I encounter earlier in the year - there are one or two ports shown on the map that are only needed to get around rocky areas when the water is low that I didn't use.  The map does not show all the portages  (there are maybe 8 or so) - the critical ones are pretty easy to spot.  I recall one of the portages being hard to find in the upper half, due to blowdowns obscuring the landing (that one was a short portage on river left).

there are several old threads on this topic- do some exploring in the old trip reports and use the search feature with the search parameters at max exposure