Interesting; a lot to think about. The pro I just started working with doesn't know lick about obedience and my obedience trainer knows very little about field (she has dabbled with her dog, but not competitively). So... That makes it a little hard for me to try to figure out the best route. I have a soft dog that shuts down when he is confused, so I need to make things as clear for him as possible.
The cool thing about field work is you don't have to re-invent the wheel. The tried and true "Lardy flowchart" method is what 95% of the people running senior & master use to transition their dogs from beginners to running blinds. This is a foreign concept to pure obedience people, because obedience is much more linear and intuitive and people really can cook up their own methods and be extremely successful in competitive obedience. There's no "one way" to do it for obedience. In field, it's a different scene. Now I'm not saying that you 100% must follow the modern method of retriever training (Lardy) to get a good field dog but it's overwhelmingly popular, most people follow it in some form or fashion. It's repeatable.
So what I'm getting at is, I 100% understand the frustration of the unknown and thinking you need to form a battle plan to address obedience vs. field, but really, like I said, keep your obedience obedience and your field field. If you've found a good field instructor, stick to what they say and don't ad lib. Hopefully they follow some form of Lardy so you can also read the Lardy manuals and the other media sources out there that basically follow the same training schedule (Graham, Stawski, etc).
The confusion issues you mention with taking back vs. over casts vs. directed jumping and drop signal, and conflicting commands such as heel or back, are all very temporary niggles of confusion for the dog and won't be big issues, I promise you! The dog will work it out quickly if you're consistent. Bigger issues you will have to conquer for a crossover dog:
1) Eye contact as avoidance. Obedience dogs are taught from day one to give constant eye contact. The only time we want eye contact in field work is in the holding blind and on a sit whistle! Other than that, the dog's eyes should be in the field. Many obedience-first dogs will "bug" (look up at you) as a default if they feel nervous or are avoiding their tasks in field work.
2) Pile work vs. scent articles. My two dogs that were cross trained had opposite problems. Fisher learned Utility before he ever did pile work, so was a terrific shopper, and I wasn't willing to correct the shopping in field work because I didn't want it to mess up my articles. I just lived with it. With my next dog who did field first, I nixed shopping right off the bat. If he feels the heat in training articles his tendency is to grab the first one he comes to. Dogs taught pile work first will often view a pile of articles as a RETRIEVE exercise not a SCENTING exercise. Different problems to tackle.
Actually those were the only two biggies I could think of...
One last thing.....
Be prepared to not get away with terms like "soft dog" "shuts down when confused" etc with modern retriever field trainers. While we are certainly sensitive to each dog's unique personality and learning style, and adjust training as needed, "soft" "shuts down" etc are key words for AVOIDANCE - LACK OF EFFORT - MANIPULATIVE. A dog who "shuts down" simply because he is asked to do something he's never done before or asked to do more than he wishes to do, has simply learned to play dead to avoid work. It won't fly in field work. The good news is field is intrinsically more rewarding than obedience ever thought about being, so unless the dog is a total slug there's almost always something in it for him that keeps him going. But when push comes to shove -- doggie must do as told, not roll over and be a marshmellow to get out of it.