I have a '99 f250 with a 7.3
I won't try to tell you what I think you need or what you should want, that's something for you to decide. I really like my 7.3 have had little to no problems. The worst was a timing sensor. A good site for information is "diesel stop"
I put about 3000 miles a year on mine and I don't change oil based on miles, I know its not the most efficient but I will change oil based on time usually once a year some times twice. I only use it to tow, and it gets used hard 3 or 4 times a year.
Im not sure about the 6 liter but on the 7.3 the intake could use upgrading and I also upgraded the exhaust. I went with DP tuners with their 40hp towing tune I couldn't ask for more. One thing I would like to suggest, and that is gauges, exhaust temp, trans temp and I have boost but I think you could do with out it if you want.
good luck with whatever you choose
There is nothing like the smell of diesel in the morning!