re:(4)
Mary's the PRS member so I'm not the expert.

First: yes, as I said PRS credits performers' own arrangements of trad material in the same way as a singer performing his own songs.

Second:
We fill in PRS forms for festivals where we're booked guests. That's straightforward: you collect the forms at artists reception, and if you're efficient (as Mary is!) you fill them in as you go and hand them back at the end of the festival.

For guest bookings at folk clubs we use the "small gigs" scheme. For that you can do the return online, and it's modelled on the assumption that you have a more-or-less fixed set list which you perform at each gig. (I'm not sure how variations are accommodated). The venue doesn't have to be involved at all but is mentioned in the return. It is possible that a venue that isn't paying PRS license fees and gets flagged in many "small gigs" returns might end up being chased for license fees by the PRS, but one has also to consider that the PRS doesn't have the human resources to bother much with that until the amounts are significant.

For sessions and singarounds we don't do anything. The venue (e.g. pub) may be paying for a PRS licence, for a variety of reasons as suggested above by others (recorded background muzak etc.) and it's a one way traffic as far as I can see.

We do get returns from use of our three albums as well. The details (which are listed and sent to us by th PRS) are interesting. Occasionally a track gets played on the radio, and apparently one song is popular at an aerobics class somewehere and there is also a small blip of usage at a (non-folk) dance club. The mind boggles...

Did you have to get your return endorsed by the licence holder?what sort of money are we talking about?
I think you have to do that once with your get your "small gigs" list to demonstrate that you are a professional gigging musician. As for amounts, quite unpredictable but as I said the cost of membership was covered by a couple of festivals and a handful of other gigs in less than two years, and from then on it's all profit (that has to be declared in the tax accounts!)

If you're mainly doing it as a pastime, it might take a few years to get a return on your investment.

Anyway, don't ask me, ask the PRS

The system's not perfect, but it's probably the best approximation than can be done with limited resources, and it's a lot better than it was. The PRS has had a bad reputation, and that was well earned in the past, but it's had to pull its socks up since then.

Anahata