I'm a dealer with warranty experience.
1. Your warranty being voided is EXTREMELY RARE. A dealer CANNOT void your warranty a maufuctor has to do it. Here's how the process works.
A. Dealer thinks you caused dmg to vehicle therefore voiding warranty, dealer contacts Ford who sends out a tech to do an inspection.
B. Tech will determine if Ford should void the warranty or not.
When it comes to things like Oil changes etc it's pretty obvious between those who do maintain their cars and those who don't. Also their is a wide safety margin built in. Like lets say it says you have to do an oil change every 10k miles or 1 year. Well if you do 10k miles in 14 months your most likely going be ok.
The one time I saw a warranty legitmately voided was a Ford Mustang GT. A lady bought it from me and drove the living crap out of it, somewhere in the 20,000~ mile range her engine blew. As the tech told me the oil was basically non-existent at that point. She was somewhere north of 20,000 miles. Her warranty was voided.
Another instance (female ironically) didn't change her oil, it wasn't as obvious and Chrysler told us if she can have a mechanic (any mechainc) write up a letter saying that he maintained the car they would repair her engine. She of course was a moron and didn't do that. By the way we lined up a mechanic he was going do it free of charge too. Her engine recently blew and she's out of a car. She truly is a moron...
Per who changes your oil, doesn't really matter as long as the person whose doing it knows what they are doing. Your grandma can do it, you can do it, a dealership can do it, hell if you can teach a monkey to do it they can do it too. The only time this will be questioned is if it's obvious it was done WRONG. Keep receipts that's always handy.
For you car nuts, 3,000 miles not needed, 5,000 miles not needed. Change your oil when it asks you to change its oil. if your sales person says "Every 3,000 miles' pay close attention cause he'll prob follow up with "And our service techs are some of the best in the business". No it does not hurt to change your oil every 3,000 miles or whatever your rule of thumb is. But it's like refilling up your beer mug when it's 3/4 full, doesn't really matter.