Keep in mind there is a difference between basic double skills and technical double skills. For the technical skills, definitely take a course and don't learn from Youtube exclusively (obviously you can look for inspiration). But for the more basic skills, there is a good argument to be made of getting comfortable with doubles in your own time.
As somebody said before, diving doubles recreational isn't that different from single tank backmount. The biggest difference is the bulk of the equipment. That will obviously effect your weighting, trim and buoyancy, so you need to relearn that. Luckily, this should all have been covered in your OWD training, so you already know how to do that.
The next big difference is probably the long hose. There is no reason you can't use a longhose on a recreational, single tank backmount dive (even with a jacket BCD) so why not get comfortable with it there? Donating (or even taking) a regulator in an OOG situation was covered in OWD, and again in your rescue training, so I have no doubt you can figure out the basics in order to do a recreational dive, and then learn the finesse in your technical class.
Just take it slow and make sure you do some dives with every substep you might take. It could be something like this:
- Jacket BCD, single tank, octo regs >>> BPW, single tank, octo regs (do a few dives till you are comfortable)
- BPW single tank octo regs >>> BPW single tank, longhose (again, do a few dives)
- BPW single tank longhose >>> BPW doubles (do some dives to hone in buoyancy, trim and weighting again)
Other stuff (like valve drills) is best left to the technical class, because that is something new compared to recreational diving. And for what it's worth, it should be covered in your tec course so no worries there.