Türkiye needs immigration. There is no need to send all the Syrians back. Young, educated, adapted ones can stay if they wish.
My young Syrians friends are totally inseparable from Turks and they refer to Türkiye as "us/we". They are already Turkified in my opinion. I can see their kids in future saying things like "bizimkiler de Halep göçmeni". It will be just like Albanian, Circassian, Bosniak migrants in our society.
This injection of young people will benefit Türkiye's demographics and it will strengthen our bonds with the future Syria and the Arab world.
A big win in many dimensions.
We could use them to exert influence in Syria.
The end goal, apart from destroying YPG, should be to make Syria dependant on Türkiye and make it a mutually beneficial relationship. We should train their military, arm them, make them use our currency, sell them our products, etc.
It's good that Jolani seems to be open to secular rule. We need to make sure that if they become a vassal state, they adhere to our principles. If they go full Afghanistan then in a few years they'll get carved up by a coalition once again. A historic opportunity is presented to us, we need to play our cards right.
As for keeping refugees. I've seen what this has done to the west. Trust me, demographics are fucking important. If in 50 years Turks become less than 50% of the population, the country will be screwed. It's best if we secure Syria, give it similar laws and living conditions to Türkiye, and encourage as many Syrians as possible to return.