For many of the heroics, only your tank being geared matters a lot. And the good thing about that is you can get your tank into about 2/3 epic gear, maybe 3/4, the moment you hit 80 with a decent amount of money. As a multiboxer, making money is trivial at worst, so getting enough to just throw epic gear at your characters shouldn't take too long if you just finish all the quests in storm peaks, icecrown, etc.

Funny enough I just finished leveling my Druid solo boxing to 80, and I actually dinged 80 about halfway through zul'drak, leaving me half of zul, all of sholazar, storm peaks, and ice crown for leftover quests. If I could have done this x5 multiboxing it would be a crapton of money. Even as a solo boxer its quite a lot of money left.

Just something to think about. Now if you dont have the money or are unwilling to spend it, then jumping right into a heroic as a boxer at 80 is very tough. My recommendation is to at least get 5 epic weapons, and then buy every tanking epic available at 80 (valor bracers, tempered titansteel gear, titanium earthguard gear, etc).

IMO any way you look at it pugging heroics on 1 character is just way, way slower than multiboxing heroics. Unless you get a really good pug group, which you probably won't if you just hit 80, it will take you at least as long to pug 1 heroic as it will take to complete it as a multiboxer wiping 7-10 times during the run