I have a few questions about exam process

I have a few questions about exam process.

I’m starting preparation to USMLE step 1. Would like to take the exam around May-July. I think it’s enough time from now.

As I understood first I must register in ECFMG to verify my university, right? How long does take that process?

After my application is verified do I have to register for step 1 immediately?
While submitting application for step 1 exam do I have to pick a date and place of the test ? Is it easy to change a place of examination center?
What if I’ll wait with all process and register later? Are the places limited?
If it’s better to apply earlier I’ll do it now. I did a research but didn’t find satisfactory answers.

Would be great if anyone could help