Whatever I can do to help, everyone on this forum is excellent like that May. I do use topical Regaine, and the liquid not the foam as I believe its more effective, and likewise with the oral I'd rather apply it direct on to the area, although when I get time I will do research on the oral version to compare efficiencies between them as the liquid does leave a bit of residue and disrupts the hairstyle (not that I really have one at the moment though). Its hard to say how much of my result is down to native hairs against transplanted hairs - however I'd expect it to be as you say as the reason for me taking Regaine is for the retention of existing hairs which is as important as the growth in the transplanted hairs. I found in the 2-3 years in taking Regaine before the transplant that I didn't grow new hair..... and I can't say how much I'd retained in that period as I'd lost some which may or may not have been due to unexpected ill health needing surgery. So I can't say for certain that Regaine works for me - I'm just doing everything possible to ensure the success of my transplant.
Thats why I'd say to you that if you want your transplant to be a success I would most strongly recommend that you take the Finasteride now and throughout the whole growth stage - this isn't a time to experiment as you need everything to encourage the new hairs to take and to grow, as if the transplant isn't successful then you have nothing you can do as all your donor has been used up, and you'll have a scar to cover up too. So please reconsider and if you don't get sides from Finasteride then take it - or if not the Regaine if that did work for you. You have to do everything you can to ensure you retain your native hairs and provide the right environment for your new hair to grow as well.
If you're wanting to find out if Finasteride works or not, then the time to do that would be after the 18 months growth phase, when hopefully you've got good growth, and then you can stop taking it for a while and if you start losing your hair then you can start taking Finasteride again which should reverse the loss, however if the new hair doesn't grow in the first place then you've got a BIG problem.
If I may refer you to an example of this - a chap on this forum called Phil W didn't follow advice to take Finasteride/Regaine and to say he deeply regrets it now is an understatement. Not all the new hair took but he also lost native hair and now he's left with an island of odd looking hair and also two scars on display at the back of his head.......... I hope this is taken in the spirit that it is meant as friendly advice that I would wholeheartedly recommend you review your decision to stop taking Finasteride and restart it asap.