Before doing anything you need to read, read, and read about these engines. Fortunately you are on a great site for that. There is a ton of spotty and outright incorrect information out there about these engines.
In general I would not look to modify a 6.0 truck that has not already had all the bulletproofing done. Trying to get more power out of one of these engines without first addressing the weak links is a quick way to end up with a broken truck and no money to fix it. Bulletproofing should include EGR delete, coolant filter, coolant flush, new oil cooler, replacing the STC fitting, replacing the stand pipes & dummy plugs, and a proper head gasket job with studs (heads go to a machine shop for inspection and milling). Having the FICM rebuilt by
FICMRepair.com - FORD Powerstroke 6.0 FICM Repair, PHP Tuning and Truck Parts and loaded with the Atlas 40 tune is also a wise idea. Hot side CAC boots are also on the short list of things to replace while you are in there. Cleaning the turbo is another one. Get a monitor on the truck too, something like an Edge CTS.
Once its bulletproofed you can add more power. An SCT tuner is the best option for PCM tunes with custom tunes written by Innovative or Gearhead. With a stock fuel system you can get about 425 RWHP from a 6.0. Going beyond that requires some expensive upgrades. Injectors and a turbo, which need to be paired, and once you go much bigger than a PMax you are going to start trading bottom end for top end, which on an engine that already has a fair amount of lag isn't worth it for something street driven IMO. 175cc injectors area bout the max a PMax can handle, beyond that your EGT will become dangerously high.
The trans isn't really a concern in these trucks. The 5R110 is very stout. There's no need to think about upgrading it until you are nearing 600RWHP. I run a Ford reman trans that has over 120k on it without issue making over 500RWHP.