If I set PL to use a 60 min log file instead of the usual 1 min one - how will this affect PL?
You will have to wait until the each hour has finished before you will be able to access it in client. With 1 min segments you are only ever 1 min behind real time with the client.
How can I be sure it will rollover exactly on the top of the hour (at show-change)?
You would have to ensure that the PC clock is synchronised with the clocks in the studio. Do a forum search for articles about time syncing PCs.
Is there a script or util in PL that can collate all the logs between x and y time and concatenate them into a single WAV file ready for further processing?
Can this functionality be added in next release? It's VERY similiar to what PL does already... I just want it to make show length (usually an hour) MP3/WMA files, name them and put them in a folder ready to upload etc.
This is not something that v3 can do. It is however a planned feature for v4. Also, v3 can not handle anything other than wav files. This is another limitation that v4 addresses.
Of course, if you go with 1 hour segments then you already have your shows in separate wav files and you could automate a command line encoder to convert to another audio format. There are many free ones out there including Windows Media Encoder.