Please tell me all the possible ways I can earn some bitcoin,
as a developer.

I can write C++, Rust, and Go.
I want to use this capability.

What type of Ethereum project do you recommend me to join now?

I have successfully set up a PRIVATE CHAIN with geth, but
I am not sure what to do next.

To make money.

I forked from bitcoin and create own coin.
I want to implement SPV wallet for it.

Thank you for reply 
I try soon

I made bitcoin clone from source code.

I mined 1 million coin.

I try "sendtoaddress" to windows wallet not synced whole blocks,  but it not working.

If I want to use sendtoaddress command,
do I have to sync every 100,000 block on windows wallet?

I have other vm on ubuntu wallet fully block synced , no problem send and receive coin.

so...

if I want to send coin to new user, he must sync whole blocks?
but its not useful for him.
he will stop using my coin.

I want to send coin without waiting sync. How?