Gary, there's pages of Disco prep just down the screen and lots more on here if you do a search. Tour operators also do good checklists. I assume it's a 1 or 2.
No to snorkels, winches and fridges. Extra cost and weight that you don't need.
Maybe to dual battery, but what you going to run off it and where do you put the battery if you don't fit a snorkel (if its a 1)?
Yes to servicing, diff guards, replacing mechanicals and electrics that are not in tip top condition, and personally, the roof tent. The most important thing for a solo trip is peace of mind, so spend money on things that could go wrong if you don't.
Cost of good shocks is insignificant in terms of what the trip's costing you in fuel and ferry. Good shocks are essential on a Disco.
Your tyres will be fine, as long as they're not re-treads.
It's all personal opinion of course, and someone else on here will tell you I'm completely wrong!