If you just received your AmEx Gold, you need to be putting spend on that card anyway to get the SUB, right? After you've met your MSR, then for groceries it will depend on what you value an MR at. Pure cash out as statement credit 1MR=$.006. If you have a Schwab Plat then 1MR=$.0125. Or if you have certain stores that you wouldn't mind a gift card to, then
some of those gift cards are redeemable at 1MR=$.01, you'll have to do the legwork to figure out which ones. For example, Home Depot gc are 1MR=$.01 (with a min 2500MR redemption) but Apple gc is 1MR=$.0085 (min 1176MRs). If you're in this for travel, some people like to transfer out MRs to AmEx's travel partners to get airfare for higher value out of their MRs. As you can see, MRs are very flexible but also quite nuanced.
1) It may take a few days (2-4) for his status to be updated to Platinum. It will last until end of Feb 2023. The 5 suite night awards earned this year expire Dec 31, 2022. In order to get another 5 suite night awards, he would have to reach Platinum again (50 nights) in 2022, and those would expire Dec 31, 2023.
2) That promotion requires one paid night and at least two consecutive nights (as
@Judique was kind to share) to count as a stay. You should get the double nights promotion on the one reservation that is two nights long (as long as one of those nights is paid). I did a dummy booking locally, and was able to apply free nights to 2 out of the 3 nights by picking "Customize Payments." Are you sure that there is availability for free nights on the dates at the place you're planning on staying? The times I've not been able to do "Customize Payments" has been when there is no free night availability due to capacity controls.