My car is havving problems.
 

It was rebuilt like three weeks ago.
First I had issues starting it.
It would take a min or longer.'
then
The car started droping rpms and going back up while i was ideling.
How can I fix this?

the tps needs to be adjusted, as far as the idle issue goes.

And the flooding, or hard starting, is because the engine isnt broken in yet.

How lond do it take to break in?
It's been 150+ miles

i heared its about 1,000 miles to be a goos break in. i'm bearly on 2

Keep rpms under 4k untill 1k miles then gradually up them.
In other words, don't drive too heavy, keep the load on the engine lite, no "lead foot."

What will happen?

^^ Boom is what will happen. Break it in nice and easy.

But about your problem, I had the same thing. Check timing to ensure it's right. I don't care if you dropped your CAS in the same way it came out, check the timing with an inductive clamp timing light. I actually installed my CAS drive gear backwards, which made it impossible to time. I also pulled the wires out of the connector for the temperature sensor, so the ecu defaulted to 80' F. On top of all that, the TPS wasn't adjusted, and various other things went wrong after the install. I was a noob to all things automotive at that time, so there was quite a long list of things I had to fix later that I shouldn't have done.