The list NEEDS Assault Centurions and Devestator Centurions. The Imperial Fists use loads of them - see GW's new Imperial Fists codex (Sentinels of Terra), where lots of Centurions is the core of how the Imperial Fists list differs from codex marines.
I like the +75 for 2 Vindicators
You've used the wrong list as the base and missed out the 2012 changes to the core list. Apart from those you've mentioned Predators should be 250 and Vindicators should be 225. Your Terminators are 325 when they are normally 350 and Whirlwinds 275 when they are normally 300, I hope these are mistakes also?
I think the list should keep it's distinctive Assault Terminators either as well as or instead of normal Terminators. Lysander is known to have use Titanhammer formations of Assault Terminators when going up against large enemy war engines or titans - see
here.
I think having two separate attack and defender style lists for the Fists is superfluous and a very bad idea too. No existing epic race does this - there's only one Krieg list which can both attack or defend and the same should apply to the Imperial Fists.
Fortifications and minefields should be included in the list. If transport flyers and fortifications are felt to be too powerful together (they may or may not be) allow only 0-1 transport flyer if any piece of defensive fortifications are taken (or visa versa). You could have the core list and separate sub-groupings for 'Air Attack' and 'Defensive Fortifications' that a player has to choose between when making his army list.
Having just read through the Imperial Fists Sentinels of Terra Codex the one thing which is hammered home repeatedly about the Imperial Fists is their stubbornness and unwillingness to flee from fighting, even when it would be strategic to do so. As the codex puts it: "The Imperial Fists are notoriously stubborn, a trait inherited from their
Primarch, Rogal Dorn. This can often be a burden, compelling many of their strike forces to carry on with a task in the face of all reason, and even at the cost of their own lives. At other times, though, their fabled tenacity can allow them to endure where others would have failed or turned back, overcoming terrible odds through a sheer unwillingness to admit defeat." and elsewhere "Phalanx’s librarius contains many tales of Imperial Fists who have died needlessly, driven to fight on when their Chapter and the Imperium both would have been better served by shamed, but living, warriors. Squads, companies – and if rumour speaks truly, a yet greater tithe of the Chapter’s strength – have perished in this manner at one time or another." I think this stubbornness should be represented in Epic. The way it works could be discussed but my tentative off the top of my head suggestion would be that if any Fists formation looses an assault for by one single point only then it immediately fights another round (as if it had drawn) but the enemy force gets an extra point to their assault resolution score for this (and any subsequent rounds). This would have no effect if they loose by 2 or more points and it would reflect the stubbornness in both good and bad ways for the Fists.
Imperial Fists are are noted as stubbornly taking heavy casualties and having a larger than normal recruitment drive and base of scouts than other chapters. I would suggest Scouts could be a 1+ choice in the Epic list to represent this.
I'm really keen to hear people's opinions, but as usual, batreps and experience speak much louder than complaining... try the list, you might like it 
