Hi Athena & welcome,
Well, it seems you two have a pretty healthy and logical approach to this whole process. You've put a couple very important pieces in proper perspective.
1> His preference for just some 'sexual' variation - as long as handled respectively and safely is not in conflict with your bond. It's just 'sex' !
2> Your desire to prefer to at least know and have some level of trust and respect for his partners is very reasonable and we'd say desirable. It adds to the openness and honesty which is just a much better environment for everyone.
Now..........that all being said.....
There's a couple pieces of the evolution we'd recommend you explore before you get too deeply committed to going down this path.
1> He needs to understand your needs & preferences about your own potential partners and that your requirement for a deeper bond - dare we use the "L" word - is something he needs to start processing in advance. I.E. Am I going to be able to feel good about my wife loving (and having sex with) someone else ? Easy to say when it's not real and in your face
Process now rather than later.
2>You have to acknowledge, depending on your - particularly his - lifestyles, that there's always going to be that possibility that he might find himself in a situation where sex would be an option without - if we want to call it - 'pre-approval'. For example, if he has to travel a lot for business etc. This is part of the trust issue you need to develop between you. You have to trust and believe that your feelings and concerns are foremost in his mind and that he'll use his best judgment as circumstances arise.
Personally we prefer this approach to rigid 'rules'. Although we have a 'desire' that we both know each other's partners in advance to just get second opinions if you will, we also acknowledge that we know & trust each other well enough to let things develop as they naturally will which means some 'activity' might occur before we all get to meet - at least in person. We proceed with the idea that the 'plan' is for us all to be 'together' in this, but that we're not going to get hung up over the chicken/egg syndrome.
Good luck. KISS (keep it simple, silly)