Take this info FWIW, its based upon my own use, practices and experiences with this family of motors...........
-Plugs should be MotorCraft or the Autolite equal---both are designed specifically and tend to produce the best performance and life. So far none of the claims about other brands being better or longer lasting have proven to have any validity. Along with higher costs such so-called improvements have absolutely no advantage over MC or Autolite.
-Personally I don't believe spark plugs are truly effective past 50K miles so I change them myself at that interval. Boots are inspected and replaced as needed; NAPA makes a nice part for about $5 each, Belden/USA made too!
(This interval I use will draw criticism, citing what the owners manual states however there's no harm in performing some maintenance steps sooner than suggested.)
--Along with correctly placed dabs of dielectric grease in the wiring harness connectors as well as in the tops and bottoms of the boots I use a nickel-based anti-seize on the plug threads, torque them to 21-23 ft/lbs. This too is a sometimes hotly debated issue, published specs calling for 7-14 lbs. A completely unscientific test conducted by a member on FTE shows Modular Motor heads can withstand plug torque approaching
75 ft/lbs before adverse effects on the threads. Of course this discussion devolves into what causes plugs to blow out of a head--sadly there's very, very little real evidence which practice (or lack thereof) is behind this statistically low rate of occurrence.
Depending on your skill level, tool availability and desire to DIY such an operation this is one of those procedures an owner is advised to learn and perform personally. As a disclaimer DIY can't 100% guarantee plugs won't be ejected however that possibility is reduced so greatly its well worth learning the process.
Do keep in mind these suggestions are based upon my own practices and experiences so take that FWIW.
Your other flushes and refreshes are well worth the time and money invested---keep those up!