Last date- There is no such last date for being a GST Practitioner. You can apply anytime.
Exam date - When you applied and your Application has been accepted and you have been allotted USER ID and Pswd then you are eligible to go for the next coming exam.
Job possiblity- Job Won't come to you. You'll get a certification that would certainly give you an authority. But you have to work hard. when someone seek for GSTP service then such request is forwarded to all GSTP and you have to contact and convince the client. ALTHOUGH YOU COULD USE YOUR GSTP CERTIFICATE FOR GETTING CLIENT AT YOUR PERSONAL LEVEL.
There are many seminars already going on by Govt which is freely available online(webinar) and offline( seminar). When you will become a GST practitioner then you will receive mails for every online and offline seminars.