To do List:
Drain Fuel tank ?
Unless the fuel is obviously contaminated I would probabaly not bother with this. Unlike petrol diesel does not reall "go off". It could be useful to see the condition of the fuel but if it is vaguely flammable, and nearly liquid these engines will probably run on it!
Purchase Oil filter + Install
Very straight forwards job, but if it the original paper filter you are replacing ensure you have removed the rubber seal from the top of the housing, it has a habit of staying in the housing and then not sealing properly when you try to install a new (second) one.
Purchase Fuel Filter + Install
Same as above, farily straight forward, but ensure you follow the proper procedure after installing to properly bleed the fuel pump, these do not self bleed like later engines.
Purchase coolant for engine (Water or 50/50?)
Get the concentrate blue (Monoethylene Glycol) anti freeze and dilute to the specified concentration for the brand you have purchased.
Purchase Glo Plugs (Potentially needed to start)
This is going to be very important if it is not currently starting. These engines will really struggle to go without them. I would first check that the glow plugs are receiving power. If they are, then I would look to replace, but be aware that there are different sorts of glow plugs and it depends which sort you purchase as to how they need to be wired in. I believe the newer ones are wired in parallel, whereas the older type are in series meaning if one fails all the ones after it fail as well.
Purchase fresh Diesel for engine
See above referance draining the tank, could be useful initially to use a known god fuel, but dont through the old fuel away unless contaminated as it will still be usable.
Get Engine to start (Currently just cranks when trying to cold start)
Potentially purchase bigger battery
I would only bother with this once the engine is running, for now just use a known good battery, then fit the largest battery you can physically fit in the space.
Fix Electronics
There should not be any electronics in one of these, the electrical system, especially on a diesel is very very basic, and is just a series of simple circuits for the lights. What is the current problem?
Fix windows (Driver side glass doesnt stay open just falls out because of no rubber to hold glass in)
Depending on the condition of the door top this may become a replace the door top job. you can get replacement channel that are held in by self tappers, but if the current channel has rusted away I would wager they door top it screws into has rusted away as well, and therefore you will have nothing to attach the new one to.
Paint job - Quote needed.
Don't bother with a quote, it will be more than the land rover is worth! Do it yourself, either spray or roller. plenty of people, myself included have roller painted their land rovers with very good results. clean it, rub it down, paint with etch primer, then using a foam roller and synthetic enamel roller the top coat. I can give you more details and pictures of the finished result if needed but there are several threads on here already about doing it this way.
Install new wing mirrors (Already obtained)
Very straight forward job, if tru wing mirrors (ie in the wing) they just unbolt from underneath. If they are door mirrors unbolt the door side of the hinge to reveal the wing mirror bolts on the inside of the hinge.
Install dash (Radio, Glovebox, Speakers etc.)
Don't bother with this either. With a 2.25 diesel you will not be able to get a radio loud enough to hear, just leave the dash standard, fill the tray with everything you would normally put in the glove box, and learn to enjoy the agricultural sound track that will accompany you everywhere you go.
Pass M.O.T
If it has been stood for a few years, before putting it into an MOT it would be worth checking all of the chassis for rust holes and suspension bushes, steering joints, propshafts, wheel bearings, swivel bearing/bush for any free play.