When I was testing out one of the early alphas, I ran with a party similar to yours without tactical mods, and it was pretty challenging. With tactical mods installed, and running on "hard," you're going to be in for a rough ride, and possibly a lot of reloads.
It's a shame, really, that most of the Tutu modders had dropped out of BG2 modding by the time I wrote Gavin. Crossmod would have been nice, but it's impossible without both modders' participation. But since they had, there isn't any crossmod content between Gavin and Finch, Indira, or Mur'Neth. There is plenty of interaction between Gavin and the BioWare NPCs, though, and with the PC, if that's your thing. Gavin also offers a romance for a female PC, if that has any bearing on your decision.
Finch is a lot of fun, though, and I've enjoyed playing the mod myself. Since her joining sequence involves enlisting her help in fighting Karlat, you might have some trouble getting her into the party at all. When I tried the mod, she kept dying before I could recruit her. It took several attempts.
If you're set on that party, though, you might want to try one of the fighter kits from Sword and Fist to enhance your front line, instead of your planned bounty hunter. You really could stand another melee fighter. Mur'Neth can function as a thief, IIRC, although his placement behind a couple nasty and unavoidable traps might present a challenge if you plan to run with him as your only thief. I don't know if it's necessarily a bad thing to have two clerics in the party, though, especially on the more challenging settings. Especially at low levels, they don't get all that many healing spells, and you're likely to need them.