A lot of this advice can be found elsewhere on the forum, but a few thoughts:

Step #1 - pick a program/alliance and stick to it as much as possible. There are 3 major alliances: Skyteam (Delta is the main US based member); Star Alliance (United, Continental, and US Airways are US based members); and OneWorld (American is US based member). All 3 alliances have a substantial number of partner airlines elsewhere in the world. You mentioned he flew on Lufthansa, which is part of Star Alliance; you also have obviously flown Delta before as you have some miles there.

Since it sounds like the majority of your flight points are accrued from your husband's intl business travel, a logical question would be does he get to choose which airline he flies? If he doesn't get to choose, does he regularly fly the same airline (or at least the same alliance)?

Each alliance has positives and negatives, but some key negatives to consider:
*If you go with Skyteam, Delta is widely considered by many on this board to be the most difficult airline on which to redeem saver flight awards. As in, orders of magnitude harder than the other programs.
*If you go with Star Alliance, be aware that United's program blocks availability of many partner airline flights based on the point flow between the partners and United (google "United Starnet blocking" for more info). If you are planning to redeem mainly/only on UA, this is not as much of an issue. Also, it can be avoided by selecting a different Star Alliance program other than UA's program
*All programs, to some extent, will limit mileage accrual to less than 100% of flown miles on international partner itineraries on cheap fares. AA earning on BA, and Delta earning on several partners, are notable examples, but they are out there in every program and every alliance.

You also mentioned that you like the convenience of flying out of CVG. Well I don't have to tell you that DL has cut flights from CVG substantially vs what they had there a few years ago...or that CVG's fares tend to be on the high side. But if, despite those factors, you like the CVG hub, that might tilt you towards Delta.

I can't tell you which program/alliance will be best for you. But I can tell you that no matter which one you choose, you'll fare best by picking one and sticking to that alliance and its partners as much as possible.

#2 - credit card - will be determined to some extent by which alliance you choose. If you are going with Delta, then I suggest either Delta Amex or Starwood Amex. With AA, Starwood Amex is probably best and the Citi AA cards as a backup (plus Citi always has nice bonus promos for joining). With UA/CO you are pretty much stuck getting their Chase cards as Starwood does not have a good exchange ratio for their points. Starwood can exchange 1:1 into US or into several non-US-based Star Alliance programs including Air Canada, ANA, Thai and Lufthansa.

#3 - hotels - sounds like a moot point for you as you normally stay mainly in independent hotels and your husband's business travel is non points earning. However, to the extent you may have any points earning stays, same advice applies - pick a program and stick with it as much as possible. For folks that don't have points earning stays frequently, one nice perk of Priority Club is that points never expire - the only major hotel program to offer this.

Hope this gives you some food for thought.