1. The Eligibility you are referring to is for the type of SOAP program. If you matched to a prelim year in the match, you'd only be eligible for Advanced programs in SOAP. If you didn't match at all, you'd be eligible for all types of programs -- Prelim, Categorical, Advanced, and Reserved. It has nothing to do with whether the program is new or not.
2. You can apply for anything you want. Whether programs will take your application seriously is unclear. If you applied to Radiology, for example, I imagine that the Rads PD might question whether you're really interested in Rads or not. If you apply to prelim IM/GS, add something to your PS stating that you were (obviously) applying to peds but now you're looking for a general year, they might consider you. But you might be lower on their list -- as they expect that you'll be applying to the Peds programs also and they would be your 1st choice.
3. Yes, programs will continue to interview on Wed (esp AM before rounds) and probably afterwards also. However most spots are gone in the first two rounds (at least that's what happened last year), so I expect the volume of interviews will drop off considerably.
4. Either/both.
5. Positions can ONLY be filled in SOAP. All of the open positions on the list are still open. Once they start to fill in SOAP rounds on Wednesday, the lists will be updated. For programs that decided not to participate in SOAP, they are supposed to not fill those spots until after SOAP concludes on Thursday. At that point, the unfilled list will be updated with all of the non-SOAP positions, and it will be a free for all to fill them. However, one main reason a program would not participate in SOAP is that they might decide not to fill the position at all -- so unclear how useful contacting these programs will be.