Firstly, if you completed technical training in single+pony, then you'll benefit from supplementary training on doubles. I strongly recommend that. Doubles are sufficiently different in protocol, practice and configuration that your previous training won't have provided you with the necessary knowledge and ingrained skill-set to dive them safely - certainly not at technical level dives.
I've never heard of a course that qualified/dove to 200ft using a single+pony. Some tech agencies allow their introductory/entry-level tech course (i.e. AN or Tec40) to be taught in that configuration, but not subsequent courses. Those entry-level/introductory courses don't reach depths beyond 200ft, if they have a depth progression at all. There is something dubious about that. As a tech instructor myself, I inform every student that conducting that first course in single+pony is only suitable if they wish to remain at an adv-rec level. If they have any potential intention to progress to technical diving proper, then they need to conduct all their tech training, from the beginning, in full technical rig (backmount doubles or sidemount). Otherwise, they need re-training for the equipment and procedures.
Secondly, with regards equipment, the best advice is to discuss the matter with your prospective instructor. Failing that, identify who you will be diving with the most and see how they team-rig (if at all) their equipment. As general advice, with few specifics to go on, you can't go far wrong with a standard backplate (unless you are exceptionally short or tall), a single-piece harness and a donut wing of 40-60lb capacity. Beyond 60lbs is like buying a monster-truck for your day-to-day motoring needs, and just as laughable.
With regards equipment manufacturers, IMHO:
Halcyon: Good quality, but the most costly.
Agir-Brokk: Good quality, but costly.
Oxycheq: Decent quality, but somewhat costly.
DiveRite: Often over-complicated, but a wide range of options.
OMS: The 'Toyota Corolla' of tech gear. Reports of bad customer service.
DSS (Deep Sea Supply): Excellent personal service (Tobin is here on Scubaboard and helps people with advice), good quality.