Hi 
 
 
1.    To avoid to many people, July is a good month.
 
2.    There are bridges on some rivers, but not all.
 
3.    I would recommend to take the bus to Bygdin and then take the boat to Fondsbu. That is a good starting point.  For bus: 
http://www.nor-way.no/
 For boat: 
http://www.jvb.no/bitihorn/
.
 
4.    You have picked very popular routes in Jotunheimen 
 A nice trip is Fondsbu – Olavsbu –Skogadalsbøen-Olavsbu (choose a different route) – Leirvassbu – Spiterstulen – Glitterheim and then to Gjendesheim, where you can take the bus back to Oslo. There are, of course a lot of other route options.
 
5.    Both Galdhopiggen and Glittertinden are easy to reach. Spiterstulen is a good starting point for Galdhopiggen. If you walk from Spiterstulen to Glitterheim, one of the route are over Glittertinden. There is not so crowded on Glittertinden.
 
6.    I have never been in Trollheimen, but I assume there is not that many people there 
 
Hopefully the input from me help you in your planning.