Sounds like a good plan to me.
1. SPG Biz this month, offer expires 3/28/18: 35k Starpoints for DH; 7.5k Starpoints for you. So that’s a combined $14k/3 months spend between both your SPG Biz cards.
2. CIP for the 20k UR referral to you, 80k UR to DH whenever you’re ready for the $5k/3 months spend.
The above two cards don’t count and will keep DH at 2/24. Then you’ll likely have room for 4 more personal cards by doing either a CSP+CSR or 2x SW cards double dip at 4/24.
So,
3. Sometime after April, DH could product change his CSR to a Freedom or Freedom Unlimited, maybe give it a month for the change to update with Chase and on his credit reports, then double dip the CSP+CSR. That’s a combined $8k MSR in 3 months.
Those two cards will bring DH to 4/24, with one personal card slot left that can potentially turn into two.
4. Towards the end of the year, or early next year, DH can cancel his SW cards, then go for the SW Biz, which won’t count against his */24 and one of the personal SW cards; or, he could double dip (apply for both) the SW personal cards on the same day using his last slot to get around the 5/24 limit.
The first option will leave him at 5/24, with a card dropping off in June 2019. The latter option will bring him to 6/24, so he’ll need the two SW cards from 6/17 and 9/17 to drop off in June and September 2019 before he’s under 5/24 again.
Another possibility is,
5. DH applies for the SW Biz late this year or early next year so he meets his minimum spend such that his points post in 2019. Then, he’s still at 4/24 because the SW Biz doesn’t count. 30 days after DH was approved for the SW Biz, he can still use that last slot at 4/24 to get two personal cards in a double dip. So he could get one of the SW personal cards (again make sure the points post in the same year as those from the SW Biz to qualify for CP) and apply for another personal card on the same day he’s approved for the SW personal card — maybe the Marriott personal card or whatever other new cards Chase might roll out this year.
This will bring him to 6/24, and he’ll need to wait until 9/19 to hit Chase again. In the meantime, there are plenty of Amex business cards to keep your DH busy.