is there any else to do after finishing all quest, build a base, got all npc/monster and having sex thousand times?
Could always do the classic "number go up" tism and put down as many hell totems as you can make then fight until you're uber high level.
Hang more native girls from nooses
Get tons of inventory expansion pouches from farming the kangaroo thing.
Make more android abominations that shoot lasers.
No, not particularly. Do all the quests, lament that you can't crush Little with a large rock, and play other games for a year until there are more updates.
Even modding is just build stuff I think, right now.