The principle is great, the only drawback is that your CCCH load monitoring counters (from BSS) will not work anymore. So you will have to check your Paging success% with NSS counters.
Yes, applying those settings on the whole LAC is a good bet, even though it is not mandatory.
AG PREEMPT PCH = ENABLE
BS AG BLKS = 1 (you can’t put it higher than one if you enabled the AG PREEMPT PCH)