The ones having issues with the 6.0 engine are the ones that can't leave the engine alone. We had 10 of them in Supercrew 4x4 form and had zero issues with any of them. And trust me, many of the drivers only knew two ways to drive them, completely off the throttle and flat on the floor. Hard to beleive any engine could survive the 500,000 miles we put on them. The engines never got the reflash either. Ours had the multi-injection cycle thru the entire life of the trucks.
The 7.3 is noted for being a long life engine. When it starts burning oil a simple parts and hone is usually enough to overhaul one. Rarely will you ever need to bore or even replace the block. Just hone the glaze off of the cylinder walls and replace the wearables. I'm not a fan of the 7.3 although you can't argue with the fact it's extremely reliable. It really doesn't do anything great, it's slow by comparison to newer ones, doesn't have the grunt of the newer ones, is not nearly user friendly as the newer ones, and it has a habit of burning far too much fuel. It does not use DEF which can be a headache but you'll need to watch the fuel you buy. NEVER put generic diesel in one. The injectors rely on sulfur in the diesel to soften the impact of the pintel. The newer diesel fuels have reduced the sulfur and it can be an issue with excessive injector wear. You need to be aware of the oils available for diesels. I would strongly suggest you find Delo 400 LE ONLY. The issue is the additive package for the new oils has changed considerably. You'll find the newer oils have reduced amounts of zinc, phosphorus, and sulfur. Some of these have been reduced by 50%. You engine was designed with the additives in mind. Wear will be increased by using a CK rated oil and engine life will be shorter. They make different Delo 400 oils. Us ONLY the LE and it can be a hard find. Ford has now issued a service bulletin that no Ford diesel is approved for the use of the newer CK oils. If you have Motorcraft Diesel rated motor oil in your area, it's formulated to be used in any Ford diesel. Look for the Ford certification on the bottle or the CJ rating. If it carrys the CK rating, you cannot use it unless it's an emergency and then change it as soon as you can get the Ford approved oil.
I hope you like the truck. The engine will probably last a lot longer than you're going to want it. But I will tell you, it's not a cheap date to own one. Oil changes by the gallon and the cost of filters is a killer. Might consider a by-pass oil filter for extending oil changes. The FS2500 or even the Amsoil unit will filter to 3 microns absolute. The only thing you have to worry about when to change oil is the acid build up from combustion processes. An oil report from somebody like Blackstone Labs can help you trend the oil changes.