GTWF requires 11 BAB. 18/2 wiz/monk reaches 10 BAB by level 20. If you want the full TWF line in heroics, you'll need to splash 2 more monk levels, an additional 2 of any full BAB class, or just splash 2 fighter instead of 2 monk and take GTWF as a bonus feat at 20. Alternatively, you could use an epic feat for GTWF, which would leave us with ruin, GTWF, and 1 other epic feat (probably great int, epic spell focus, or overwhelming critical).
You might also lose 2-4 points of con so you could get enough dex (and maybe str/wis) for the TWF feats, maybe PA, and boost wis for stunning fist DC. With the 2 monk bonus feats you could take TWF and stunning fist. With Harper's know the angles (half int bonus to damage and tactics), stunning fist DC would be pretty decent.