I'm sort of in the same boat as you, though not really.
We purchased 6 vials of our son's donor at the beginning of this year so that we'd be able to try for a bio-sibling. Right now we're charting and will probably be TTCing towards the end of next month.
: I've checked the site recently and the donor is currently not available. I'm scared to contact them for fear that these are the only samples we'll be able to get. I think I would feel more comfortable with 8 samples.
My advice would be to of course buy the samples! We're going back and forth about 1 or two vials per time. I think we came to the compromise that we'd use 1 sample for two months at around 32 hours and then if that didn't work, do two samples for the next two tries. At least that way we'd have one extra month to try if more samples are not available. Even if samples are available, ours cost I think $610 per try now. Crazy!
We're doing at home IUI's. We were successful using 2 samples spaced 24 and 32 hours post a positive OPK when I got pregnant with our son.
what I would say is to get a consistent routine down now. I know when we TTCed our son, I thought I'd try some 'potion' for one cycle and instead of lengthening my luteal phase, it shortened it. I tried to get healthier by exercising more, and it made me lose weight and my cycles went from 28 days to 34 or more. So if you're going to add herbs or supplements or change anything abut your diet, medications or exercise, I would definitely try to consistently do whatever you're planning on doing for at least a few months with diligent charting.
OPK's work well for me too, but so does 'cervix gazing'. We're trying to not waste any samples by making sure that everything is lining up properly before we even start again. Right now I'm charting temps right around ovulation and once the OPK starts getting a little bit more positive, my partner's checking things out up there as far as cervical position and how the CM looks.
I guess my best advice is to try not to jump the gun before you know your body completely. Has your luteal phase been pretty steady? I know sometimes the thyroid can make things a little goofy, so if possible you might want to have that rechecked before you start.
I wish you luck on your journey.
How great that you're being given this opportunity with a retired donor!