1) Glad your happy with your purchase.
2)The PAS fluid bounces around when hot. Perfectly normal.
3) Not sure on your steering issue, my 01' is tight like your 99', so I can understand your concern. The "tight" steering feel attributes to the awesomness of a Disco.
4)You could purchase the base model without the sunroofs.
5) Your clutch fan could be failing. Mine just started doing the same thing this last summer only at idle. As soon as you drive, the temp cools down immediately. That has to do with air flow. Could possibly be a radiator issue also.
6) You mentioned hearing a "sloshing" sound. That is air in your coolant system. Fix the leak, and bleed. This could also be why your temps are climbing.

 

Ahhh I see where you're coming form now Manbeer... I can appreciate that idling when you have a cooling system that is not working optimally can be a big No No. Most "Rover Guys" would probably ensure that their Discos have properly working cooling systems though rather than trying to band aid the issue by not idling.

Don't the 03/04 Discos have different part numbers for the steering boxes? Maybe there's s difference between the two. You also might need to bleed the PS fluid. I had a Disco 1 once that had violent sloshing in the PS reservoir. A couple of months later the PS pump failed... not sure if the two were linked though.