I usually have a pathologic desire to read every paper I can touch on various medications, but to be entirely honest I am so out of the loop on oral minoxidil.
It seems like a great solution and you bringing it up a few times makes me want to look into it more, I've honestly just always been turned off by the idea of taking a small dose of something that at a larger dose is known to be so side effect ridden when I can get a huge portion of the benefit with oral dutasteride and if I so desire, some topicals.
Given your usual general knowledge, I'm guessing you've looked into it and decided the low dosage of minoxidil orally over a long period seems fairly innocuous?
The TLDR is if you aren't one of the infinitesimally small number of people who has a really bad reaction, something you'd know very early on (massive peripheral swelling) you can take it indefinitely with little concern. If you've used the foam, enough has gone systemic that you'd know if you're prone to having this issue.
2.5mg or 5mg is literally a starting pediatric dose.
This is a very old, well understood drug with few surprises.
Like most BP meds, sides, if any, will be the worst during the first month, and as your body acclimates to regular use, dissipate to nothing after that. A little water retention is the most likely side, especially if you have a high sodium diet. Sometimes there's a slight change in heart rate, that's again, temporary.
You can expect increased hair growth, and improved hair quality (thicker strands) everywhere. It works by dilating microscopic blood vessels, providing more nutrients and oxygen to follicles.
Start with 2.5mg for a couple of weeks and see how it goes, you probably wont have any sides.
Keep in mind it takes 4 months on average to start to see results, and improvement continues, sometimes, for 5 years before maxing out.
Expect increased shed early on, but don't worry, those shed hairs will be replaced by thicker, stronger hairs.
Lowering BP by a few (low single digits) points is a bonus.