I actually think you can carry 5 halves and adding Lam would be an excellent addition. It would allow us to possibly move on Simpkin as one of Lam or Sullivan could be 3rd hooker cover if we get desperate, or, as Tallyn hones his craft in Cup, could be the ideal 14. I actually think that's smart business. It adds both half depth and versatility at the same time whilst also buying time for the like of Galvin, Fainu and Large to develop without the pressure of having to step up too early in the case of an injury or two.
You could then move Sezer on for 2025 and still have some experience there in Lam, with Sullivan, Fainu and Galvin all a year older and more experienced themselves to fill the other halves spot.
Meanwhile, you spend the next 2/3 years looking to make a kill in the market with a marquee (or marquee adjacent) half for '26. Lam is then filtered out, or, possibly, he makes a great fist of it and can re-sign.
I think the puzzle of Sullivan, Fainu, Galvin and Large longer term is not actually that difficult to navigate. Large, the furthest away, will likely possess the skillset to play centre quite easily, Galvin possibly also, but most likely second-row bound, leaving Sullivan and Fainu in the halves. In the (somewhat unlikely) case of finding a big signing in the halves that we can't see now (a Hughes, Moses, Munster, Reynolds, Hynes calibre player), Sullivan could even transition into the 14 with Tal the starting hooker, meaning you can fit everyone in quite easily.
Obviously very speculative, but off the back of the Lam suggestion, I think roadmaps or future sequential scenarios like this are what should be commonplace in recruitment/retention.