I have a encore in 480 with the 12" factory barrel and the black on black sight just dont work for me. I have a Primary arms 30mm red dot on my H&R Handi Rifle in 44 mag that I love so I am leaning in that direction.

Within 480 Ruger range it is pretty much a coin toss, use whichever you like the best. I have dots on most of my pistols, except for my T/C's which have scopes but then they are in flatter shooting chamberings. A MatchDot would work nicely for that 480.

do you think a standard 4 screw base would be ok for the 480 or would i need to get a 6 screw base and get the barrel drilled and tapped?

I think I might opt for a red dot over a scope for the .480.
The 480, like the 44mag, is really a 120 yard gun. Not that it doesn't carry enough energy downrange but once you get out past 120 the bullet really starts dropping fast (2" from 120-130 and 2.2" from 130-140). The longer barrel of the TC will probably stretch that out to 150 or so but that is about the max I would consider...and that is shooting from a good solid bench.

A red dot is perfectly suited for 100 yard shots (2.35" center to center)

The standard base will work fine. That is what I have used on all my T/C's, clear up to the 45/70 and never had a problem.

Ultra Dot Match Dot, all the way

I have a 35 Bullberry Super 14 barrel. It currently has a 2-7 Burris on it, same scope I put on it 15 or so years ago. I have been seriously considering a 30mm MatchDot II for it. In the woods at closer range it is much easier to locate game in an UltraDot 30mm than with a scope. I seldom hunt anywhere I can shoot past 100 yards.

Bob