It's not so much a question of room at that point, as it's a question of will the dp turn out to be psychotic and end up shredding everything in the tank one day. They can be quite violent little things. If you are going to try it, you're probably best to let the shrimp gain a foothold as a colony then introduce the neons then the dwarf puffers.
Honestly dp's are best in a species only tank that's heavily planted.