BEagle
I used to teach on the proverbial FTO-operated Seneca I which we also used pretty regularly for ATOs VFR (and IFR if we had to but the door leaked, as did the windows and we used to get ice forming inside but that's a different story). The answers to your questions from our organisation were 1. Yes and 2. Yes.
1. The change in configuration when flying visual or IFR approaches 2-eng vs 1-eng was that instead of steadily reducing through Vyse at 300' and making the decision to land at 300' 2-eng, that decision would be made through 350' when 1-eng. The profile was also flown 50' higher all the way in to allow for a bit of height loss to help accelerate to Vyse (the one operating engine would very rarely produce a noticeable acceleration without height loss). The net result was that the speeds were the same at a given distance from touchdown but with 1-eng we flew 50' higher. Power settings were basically standard 18" for 2-eng approaches in the descending part (base and final) but with 1-eng it was whatever you need, count on another 4-5".
2. Extra height loss? Gimme a hell yeah! Standard first-go-around height loss for our students was about 50' 2-eng from their "going around" call, but on their first asymmetric go-around it was more like 150-200' before they got stabilised. And that with two of us and three hours fuel. Once they got a bit more proficient they could normally get it down to 100' but the poor old Seneca just couldn't accelerate without losing height while you get the gear up.
As I recall none of this was in the POH but we had operated them since the eighties so had a bit of experience with the type.
And yes, when we taught ILS approaches later on, we had the DH discussion and got them to tell us that 350' was a committal height whether you could see where you were going or not, so if it's an ILS to minima, you are physically committed below 350' so that is the effective decision height. Below that the pilot has to be sure of making a landing using normal techniques.