Event photography advice

Hi all, I have a social event to shoot next week (my first) and am after some advice. The event is basically a fund raising party for a local Russian society and is mainly for children. My wife is one of the organisers and she suggested I do some photography there as an aid to the fund raising.

I intend to setup a white backdrop and shoot high key portraits using off camera flash. The questions I have are around pricing the photos. The original idea was to shoot 3 pictures per child/family group and email the images for 1 pound (for the charity). I then had the idea to bring a printer along but it seems to do this properly you need an expensive dye-sub printer. If I go down this line I was thinking of buying the printer with the intention of doing further events and perhaps make some money out of it long term.

If I do get the printer then I was thinking of charging 5 pounds per picture (6x4) and still giving 1 pound to the fund raising but keeping the remainder to help pay off the printer. Does this sound like a reasonable pricing model or am I way off in my thinking? Is it right to take money for myself when the event is a charitable one? In addition to buying the printer I will need to rent some lights and possibly buy a larger background so their is some additional expense I am taking on. I am not too bothered about getting the money back to pay for these and am using it mainly for experience but am I wrong to be taking money away from the charity?

If I just go down the emailing route (and not take any money myself) should I just send low res JPGs to the customers - how low would be acceptable?

Finally, would I be able to use the images I take on my website to promote my future photographic business or do I need consent from the subjects (or their parents)?

Thanks for any input.