Tomb-tainted soul would probably be a waste in most arenas. At that level it's better to prepare a Faith Healing or 2, or not channel negative energy if you can help it at all (sometimes you need to be evil for a PrC though).
What you pick depends partially on the speed of the arena and if retraining is allowed. For example, the arenas I'm in are slow advancement, so I generally pick the feats I need
now and retrain later. Clerics make excellent summoners and archers, so depending on your stats you could start down one of those fields.
By the way, your book list looks identical to a 3rd-level team based arena I'm playing in right now...are you in
Wargames on RPol? =)
If you are, then I recommend taking Toughness at 3rd level.