I did it last year, but due to other commitments of people I did it with we played it at the end of may. I thnk there were 12 of us in total, so 3 x 4 balls.
We played 4 different courses (2 clubs with 2 courses each) so was quite tight on time. Our first tee off was at 6 am and I think the last group walked off the last green at about 10pm so it was a very long day. From my point of view I would say the most important thing would be prepared with food/drink, don't underestimate how long a day it is, especially if it is hot and sunny so obviously sun block and a hat. Don't take the golf seriously, inevitably you will hit some bad shots as you get tired so just enjoy the game.
Done it three times. Enjoyable and tiring. Only done it at one club on the day but would like a crack at four different ones in one day and had Blue Mountain in Bracknell still be open it may have been viable. Might have a think...