Good build idea raj.
I would take paladin lvls 1-17 and cot lvls 18-21 monk 22 cot lvl 23-36 monk lvl 37 cot 38-39 and pali 40. I think 2 monk would make it alot easier to level and I like deflect arows for free.
Cot gets great wisdom as a bonus feat so you can have great wisdom 10 with a final wisdom of 34 46 buffed for + 18 with +6 gear and div sheild ac would be.. 66ish I think. A.b. will hit 72 while buffs last and 26 extra irresistable damage while buffs last! the best part is you can use the keen cross bow for lots of crits.
Be sure to take the rapid reload feat and point blank shot.
Another option would be to forget a.c. and take 2 fighter levels pre epic to get weapon specialization.
Cots get to take epic wep.specialization if you already have wep spec from fighter lvls. I found that out trying a cleric fighter cot. crossbow user in my tester module.