"How many number next-hop support when I set the PBR"
When you set the ip next-hop value in PBR, it is not restricted to a hop count, as long as the IP address you set as the next-hop is in the routing table of the router it will be forwarded, the limitation on hop count would come from the routing protocol in use. For instance if you were running RIP, a router 16 hops away would not be in your routing table, if you set it's IP address as the next-hop, it will be unreachable.
"When I set the ip next-hop in parallel, is it possible loadbalancing per each next hop?"
No, load balancing is achieved through dynamic routing protocols, although I'm sure you could probably design an extremely complicated QoS solution to achieve this.
HTH,
Craig