Looking at your Death Star I think it may well go for a little less than mentioned above as this one sold recently for around £640 shipped, which was in better shape than yours (including the box) - https://www.ebay.co.uk/itm/Palitoy-Star-Wars-Death-Star-Play-Centre-1977-Complete-in-Original-Box-Used-/143780882362?ul_noapp=true&nma=true&si=E1toCq6PMxE1BG2DAmzPVzuQDPQ%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557
I sold mine early last year for £330 shipped which had damage to the box and no instructions but the play set was't bad - https://starwarsforum.co.uk/viewtopic.php?f=3&t=38502
It is good though that you have the box and instructions and if you put this to auction it's hard to know what it'll go for as it changes on any given day but at least the links I've put up should give you a fairly good indication to value.
Best of luck with it though and your other items if you do sell them on.
Ian