the trouble with that is most people wont appreciate that its a MATURE set-up, which i think really adds to the value, but this is rarely reflected when selling stuff on e-bay or anywhere perhaps. If i sell a full set up (which i dont bother anymore) i would always harp on about it being MATURE and no need to cycle etc, etc.
As for you stating £800 new and asking the bidding to start at £350, thats almost aiming for getting back 50% of your money, i normally settle for 1/3 of my outlay, and would be grateful with a 1/3 back.
No one will bid at £350 you will just get lots of cheeky "offers or buy it now offers" I am 99% that will have 0 bids by Auction end, how about starting at £50 and setting a "reserve", sometimes once people start bidding it attracts attention to it, otherwise it will just be sitting there at £350 with no bids.
I personally would never sell a complete set-up again, i find breaking it down might be a pain, but you get more money in the end.
But, it also depends on how long you willing to wait.
Me personally, i would definitly sell the Fluval 305, Bog Wood, Fish and UV seperately. 95% on ebay wont have a clue what the UV is for and it wont make any difference to what you get for the tank.
Ironically from past experience, you could sell the Fluval, Bog Wood, UV and Fish seperately and it wont actually make much difference in the total amount you will get from e-bay for the whole set-up.