Freelance FO's
Spam up - I think you will struggle to get freelance work as an FO. I work for a London based operator and we only very occasionally use a freelance captain.
To work freelance you would have to be OPC'd with EACH operator to be able to fly public transport for them (every six months), unless you can get private work, I think you will really struggle to get any work at all on this basis. There is also the problem that there is only a handful of TRE's in the country, and these are in high demand.
Solution - get a job with an XL operator, build experience, consider freelance when you have sufficient command experience. It is a small industry, and you will meet plenty of people from other operators on your travels, and it would be much easier!
With regards to the TR, go to Flightsafety Wichita, they have an XLS sim, you do your rating on this which will cover the XL, whereas Farnborough have an XL sim only.