What I would do in Sony's position for the launch of PS5 is launch with just one or two major first party titles, leave the rest as third party. Give a little bit more time for the other games to come out. One title per month for the first 6 months to keep eyes on the console while satisfying early adopters, along with promoting PS4 Hits.
One of the initial problems the Vita launch had was that far too many First Party titles launched all at once, often with overlapping audiences (Modnation Racers and Wipeout are both arcade racers for example). Some of these games needed more time in the oven and so they suffered, a situation I doubt Sony would want to repeat.
They'll have third party support without a doubt, so they aren't under too much pressure unless things go completely nuts (I doubt it).
One of the initial problems the Vita launch had was that far too many First Party titles launched all at once, often with overlapping audiences (Modnation Racers and Wipeout are both arcade racers for example). Some of these games needed more time in the oven and so they suffered, a situation I doubt Sony would want to repeat.
They'll have third party support without a doubt, so they aren't under too much pressure unless things go completely nuts (I doubt it).