Well, it's good that your pain is not much of a bother anymore. Just be mindful of it shoud it return. People seem to dismiss pains as meaningless, men especially, until it's too late - and I mean that in a general way, not as a scare tactic.
I have heard both good things and bad things about Nioxin, the same with Nano as well, so it's quite difficult to say if the cost is worth it - as both are quite expensive and perhaps are different based on the individual. Plus, by adding so many treatments at once, it may be near impossible to tell which one is actually working, and which one isn't. I'd start with one, and add another if need be. If you like Nioxin and can feasably afford it, then stick with it. Nizoral is still considered one of the best, and cheapest shampoo-esque treatments out there. So if you decide to drop Nioxin at some point, I'd pick up Nizoral.
Also, six weeks on Propecia isn't long enough at all to notice any kind of improvement. You'll really need to give it a year. I know it may seem long, and chancy, and it may not even take that long, but it'll take close to it. It's kind of like those who wish to lose weight, they keep checking the scale to see if they've dropped a pound or more, and are discouraged on a constant, perhaps daily basis. However, those that check it in broad intervals, say every other month or so, are less discouraged. We all want immediate results, but there's no quick fix to hair loss, or most anything, if it's to be effective. Give it time. More than likely, you will see your crown improve.
As for adding Minoxidil, I'd wait, honestly. You're young, and your situation isn't bad at all. It may seem that way to you (trust me I know, and still feel that way regarding my own situation), but in the grand scheme of things, it's not bad. And as I said earlier, adding tons of treatments at once isn't going to give you a clear idea as to what's working. Stick with Propecia, and whatever hair care system works best for you, and see what happens. And in my case, I just didn't want to mess with topical applications. My morning routine is lengthy enough as it is, and the thought of adding one more thing, especially one that was potentially messy and time consuming (at least in terms of drying times and so forth), just wasn't ideal. I also read from various sources that some people found Minoxidil to wreak havoc on their hairline, which definitely wasn't something I wanted to experience. Granted, this isn't factually sound, but it scared me enough not to try it. Plus, nothing's proven, or even all that effective, for treating the hairline, so with the crown being the only treatable location, and with Propecia having such positive press in this respect, I felt there was no other treatment I'd rather bother with than the simple once a day pill - even though I worry each and every time I pop that little pill of what it's really doing to my system.
But, your feelings are most natural. I, a year and a half ago, was ready to do anything I could to combat this terrible plague. But, after constant research and dead ends, I found that there are really only a handful of options that are effective. Most notably Finasteride and Minoxidil. One was simple, but scarier with its possible side effects, and the other tedious and time consuming. I went, obviously, with the easier of the two. While I do think I am fighting a losing battle, my balding issue still isn't completely noticable. My crown is fairly fine, though I have a cowlick right at the crown that doesn't allow for a full head of hair at that location, and though my temples are experiencing recession, I'm lucky, I guess that I have made it this long.
Oh, and yes, I completely understand your not wanting to feel guilty. Nothing is worse than feeling later in life that you could have, or should have, done something. That you should have taken action while you had greater hope - while you had a fighting chance. Guilt is a most dreadful thing. So yes, do what you can now, but don't beat yourself up if your actions are ineffective - there is sadly so little we can do in the area of hairloss. I mean, do we really have a cure for anything? So, do what you can now with the resources you have at your disposal. Try not to look back... If only to save your sanity.
Good luck to you, and all those like us...