I have just tried in IE8 on W7 - everything works, but none of the graphics display properly.
Opera, as has been said, everything looks OK, but the L/H links don't work.
Looking at the state of the coding, you may be better off starting from scratch.
As for going official, I would start off by getting the web presence sorted, and then look at accountants and contracts etc - mainly because, in my opinion, there may be potential "customers", who will look at the site, and quickly move on elsewhere. If it were me, I would expect the website to reflect the band.
As has been said, and accountant can make all the difference to whether you pay the possible additional tax or not.
You may be better off seeing a solicitor to so out a contact - you want to ensure there are no loopholes - but it also needs to be simple to understand - again, too much legal jargon could put people off.
Anyway, that's just my 2p worth.