[2023] Eco 10 - Existing server - Claims?

You get further claims on levelups of your character in singleplayer, you can also just spawn some in like you were used to with /give claimpaper and /give claimstake. The old ones are simply preserved as is and not changeable. General recommendation is a new save on major updates, though.

Yes, though that is unrelated to this topic where settlements are not enabled. You can find the setting in Settlements.eco:

"MinCitizensToFoundSettlement": [3, 12, 25],

Town, Country, Federation