I also was raised in the Bible Belt. Allow me to offer some suggestions as you get started.
1) Your husband loves you very much.
No matter who else is in his life, you are always important to him. If his experience has been anything like mine, opening ho to you about how his heart beats was likely very stressful. He's putting a lit if faith in you that you'd love him when we know many others would judge him (fairly or otherwise).
2) He asks you to try the poly life because he wants to share that joy with his beloved.
Poly life isn't all flowers and satin though. You will need each other's guidance and counsel to find good paths for the two of you and any new partners. Be glad he wants you nearby, support his choices, and don't be shy about raising concerns.
3) He is who he is, and you are who you are.
You may find that another partner is wonderful. You may find another partner is not your thing. Either one is ok. Either may depend on the partner. Just as he is not wrong for having a poly heart, you are not wrong for having a poly or mono one. You can live each other just as much regardless.
4) Allow yourself to be bold.
How awesome is it that you're a Christian woman embracing your husband as His made him? Cool, huh? You can do awesome things. That means you can also challenge some if the notions you've seemingly always had about love. You might find that a female partner can relate to you in ways that deepen your feeling. You might find another make partner can highlight ways in which you and your husband are special. Be home and try out thus new freedom you share.
5) Be supportive.
Being poly is hard. Luckily, we try to have many folks around to lend suport. ;-) Hiwever, noone's support is more important than a wife's. You don't have to be poly if your heart is not built that way, but your acceptance of his poly nature means the world.
If you're really working on #4 (being bold), you might consider asking hubby who he has in mind as potentials. Talk with him about how they fit in with your lives and what you'd each like from them. You might even suggest that the two of you talk ti the potential together in offering an opening (it reaffirms your togetherness and mutual support).
Best of luck, and peace be unto you both! *hug*