Tower Shield build 3.5

[Koucarrots]

Basically what the title says. My GM is letting me shield bash with the Tower Shield, and we've basically combined it with a Great Sword, so now it can switch between the shield and the sword as a free action (with the flavor that it's actually the shield that's doing the cutting. Yeah, don't ask why). Playing a Half-Giant with the following stats:
Str:20
Dex:12
Con:17
Int:13
Wis: 12
Char: 11
Starting at level 6. Also bought equipment with the 13,000 you get from starting out at that level; Full Plate, Buckler, Ring of Protection, and of course the Tower Shield/Great Sword, for a total of 26 AC.
What I'm not exactly sure of, is if I should make use of the fact that I'm a size larger for stuff like Bull Rush, or focus more on making damage with the Great Sword. What do you guys recommend? I can also take flaws starting out.

[Venger]

check out Person Man's handbook (http://www.giantitp.com/forums/showthread.php?123630-3-X-Person-Man-s-Guide-to-Shields) for everything you could ever want to know about shields

[RNightstalker]

What I'm not exactly sure of, is if I should make use of the fact that I'm a size larger for stuff like Bull Rush, or focus more on making damage with the Great Sword. What do you guys recommend? I can also take flaws starting out.

At 6th level, how much longer are you going to be a size larger than your opponents? Might be worth focusing on making more damage, especially if you can convince the DM that it's a double weapon and TWF rules will apply.