I normally lurk the LS side on here but as a performance shop owner I have done many nitrous setups and built quite a few 4.6's so I can probably help a little here.
I prefer using a wetshot of nitrous myself. Using a 100 dryshot is fine though too. There are many arguements made for wet or dry so it comes down to shot size and use that would determine wet or dry.
You will need an RPM window switch and a WOT switch also. What I suggest doing is just buying one of the inexpensive progressive controllers. FJO Racing sells one, which is the one I used for my nitrous system (before the custom turbo) and NOS makes one also. There are many other makers of some pretty crazy controllers but these two are great items and pretty good price. You only spend about $20 more than if you purchased a WOT and window switch by themselves but you get so much more adjustability (WOT, RPM activation, progressive ramping, time based ramping, dual shot controllability and so on). The FJO piece goes for around $206 when I bought mine last year. The NOS is pretty close to the same price. I do not have any experience with the NOS brand controller but I have heard it is pretty decent.
Go
HERE for the FJO Controller info
Go
HERE for the NOS Controller info The link is to the JEG's site for informational purpose, but you can get better pricing elsewhere.
The stocker 4.6 engines can take a 125 NX shot no problem. NX rates all their shots at the rear wheels so that is more like a 150shot with most other brands. Running a 100shot on your Mark will be fine. The things to pay close attention to when setting nitrous up on a mildly stock vehicle are the fuel system and the tuning.
Dryshot: If you are going dryshot then make sure your fuel pump is not working too hard and that your injectors are upgraded. With a dry shot you may be able to get away with using the stocker injectors while just increasing your injector delta, but it would be better to run a slightly larger injector. I run 60lb injectors (much larger than you would require) in my other street/track vehicle and zero driveability issues so don't worry there. You will also need a dedicated nitrous tune that you will have to flip back and forth from. Your nitrous tune will be commanding much more fuel in your MAF trans table and retarding your spark timing a little as well. If you run your nitrous tune while not spraying you will be extremely rich due to your tune still dumping the extra 100hp worth of fuel into the engine.
Wetshot: If you decided to go the wetshot way then you will not need to upgrade your injectors as your nitrous is getting its additional fuel through a different avenue. You also will not NEED a dedicated nitrous tune. You can just run your N/A tune with timing bumped down just a little bit while still running 93-94 octane fuel. You get your proper A/F's through your fuel jetting in the nozzle so your A/F's on the nitrous aren't being fully commanded by the tune with a wetshot which is why you can get away doing this. Being that you will still be getting your fuel from the stock fuel system before the injectors you will still need to make sure that your stock fuel pump will support the size of shot you are going with.
In most stock Ford 4.6 vehicles their stock fuel pump will be able to handle a 125 shot (non-NX brand) before getting sketchy. So if you want to run 100 shot either wet or dry then you should not run into any issues. Of course it never hurts to throw a bigger fuel pump in there for more safety. I pulled the 100 shot out of my rear because that is the typical shot size most people go with on a stock bottom end 4.6 so I will assume you will be doing something similar.
I hope I didn't confuse anyone. I probably went into more detail than you wanted, but I figure it is better to over-inform than under-inform. I have no idea how much or how little you know about nitrous so if you already know 3/4 of this stuff then please don't shoot me.
