I was taught that when we come to a structure like this:
"...
do +
is +
(to infinitive) + particle", we usually reduce the "to-infinitive" (surely, it is not wrong for you to keep it anyway)

For example,
(i) What I want to
do now
is (to) watch TV and have snacks.
(ii) All she
did was (to) give me a hug.
So the answers to your questions are:
ALL CORRECT except one
The first thing I will do is find/to find/(A complement)finding a job for me.
- My aim is find/to find/(A complement)finding a job for me.
- What I really want is find/to find/(A complement)finding a job for me.
- What we are doing now is help/to help/(A complement)helping the poor.
- What we have done is help/to help/(A complement)helping/(
helped X) the poor???
Hope that helps, Balázs. : ) (Forgot to tell you I'm not a teacher)