I would sign up for the Amex SPG card now - I'm not sure if there's anyway to get them to extend the 30K offer to you which expired at the end of June, but maybe someone else can comment on that.

I would plan to get the Marriott card as well, but I would wait until the bonus is 70K. You may want to look into the travel packages for a longer-term redemption idea which include a week at a hotel plus miles essentially transferred out to an airline 1-to-1 (United gets a slightly better redemption).

For Hilton stays, I think you can earn miles on your stays instead of HHonors points so you could change that in your HHonors account after setting one up.

As far as airlines, it is going to depend on routes. Living in Chicago, I've flown AA/oneworld credited to AA about 5x as many miles as United - I think I even have more flown Delta miles than United. I usually go by price for the dates I need, and I'm willing to pay a little more for non-stops and more convenient times.

For car rentals, would you prefer to have a card which makes you not have to file any damage claims against your own insurance? If so, I believe the United card (cards?) is one of the only currently available cards with primary coverage in the US. (I'm also assuming you DO have a car and car insurance - if not, you may need to purchase additional coverage.)

After you get those two cards, it depends on your goals for how you (and probably your wife) want to redeem your miles/points in addition to any travel benefits. You travel to see family in the PNW each year? Consider the Alaska card to get an annual companion voucher (last year there was a 50K offer I'm waiting on). Fly to other midwest locations? The BA card (was a 100K that I'm planning on getting if it comes back) could be great - 9000 Avios round trip on American Saaver flights under 650 miles. Would rather redeem on a first-class luxury trip to an exotic locale you never thought you'd be able to take? Look up what your options are to make it happen!

Are you planning to apply for a mortgage anytime in the next 1-2 years? That may make you want to stick with minimal new cards - with 2 hotel options which both have some way to transfer to airlines (Marriott only efficiently through the package option), you'll have a decent number of options, and you'll have access to Amex Offers yet also have a Visa which is helpful as sometimes Amex isn't accepted.