Would my build be able to handle AV?

Boxing just makes me laugh. Shadow Punch is 57.8 damage in 1.056 seconds for 54.7 DPA. Boxing is 47.5 damage in 1.32 seconds for 40.0 DPA. Boxing is worse damage and takes longer. Plus, it deals pure smashing whereas Shadow Punch is mostly negative energy damage which is a substantially less resisted damage type.

I got rid of Shadow Maul because there just isn't space. You'll also notice that I didn't take Resilience either (I do like to take Resilience as a level 49 power pick as a hope that, eventually, Castle will put some of the much needed and wanted debuff resistance into it and I don't want to have to respec around that). In order to get the ST attack string and everything else that needs to be packed in, something had to be given up. Having to add Shadow Punch to get the attack string got rid of Shadow Maul and having to take Web Grenade got rid of Resilience. It's a big game of give and take.

I wouldn't say "necessary", but it would be nice, especially since it doesn't look like you'd be springing for the additional 2 LotG +rech IOs (since you're not springing for the similarly priced Armageddon and Hecatomb IOs) which was the entire reason that I replaced Fitness with Concealment + Super Speed.

Packing more than 2 endurance recovery tools isn't really necessary, but, then again, it's very nice especially when you want to run all of your toggles (including the normally prohibitively expensive FA) or don't want to bother with using Dark Consumption and MoG at every available moment.