Welcome to the site. It is scarey and exciting when you decide to go for isn't it :D
We also had to go through TRA and as Greg is a metal polisher there are no qualifications so all experience based also.
We had about 60 pages of info plus 4 stat decs by the time we had finished. Two of the companies that Greg worked for had closed down so we were unable to get references. We filed a stat dec for these detailing the work and training that Greg had done and requested a National Insurance history report to provide back up that he had worked there.
He has been self employed for the last 4 years so filed another stat dec for that and got references from 3 customers and 3 suppliers and sent a few invoices/bills etc to prove his company existed.
We used an agent too and found this is when they earn the most of their money :D Good luck with your adventure and let me know if I can help you out with anything!!