Hi mate. You don`t really say what standard you are, or if you`ve ever finger picked before, so I`ll just start from the start using my experience as an example. Forgive me if any of it sounds patronizing. First off, I`ll just tell you a bit about how I got playing Andy`s stuff.
I`ve been playing guitar since about 2000, but only on and off, a bit like yourself in that I should have been much better with that time behind me, but I`d never ever had a formal lesson, and I`d never really learnt how to teach myself effectively. That last point is very important if you want to get into this stuff.
A little over two years ago, I`d never really finger picked at all, then I saw Drifting on You Tube. To be honest, I was so blown away, I nearly gave up the Guitar because I thought that playing like that was way beyond anything I would ever be capable of. I was wrong. That is also an important point. I`d nearly failed before I`d started because my attitude was wrong, (that`s maybe why I hadn`t progressed much over the previous 7 or 8 years). Then a saw an Israeli kid on YT with a Drifting tutorial, and just had a go one night without planning it at all. I spent an hour or two getting a smplified version of the groove down, only a little section of the verse, but by then I was totally hooked. My guitar spent the next 3 months in DADGAD and I didn`t play a single note of any other tune. I was like a man posessed. Took me about an hour or two every night, but hearing the stories of others, that was quite a bit longer than average. I only had a shitty £100 Takamine at the time, you don`t have that kind of limitation
Anyway, once I`d broken the ice like that, my attitude was "well, if I can do that, I can do anything". That`s important. If the other guy can learn to play it, why the hell can`t I? The answer is, You can.
To address your questions directly...
1. Yes. Don`t even bother trying to learn this stuff in Standard because the whole essence of the song will be missing. It`s a little confusing to start with, but if you get yourself a guitar tuner, it will help you along in the early days no end. Something like this...
As for popping strings, it`s just par for the course I`m afraid. It won`t really happen that often at all, and usually only when you`re tuning above standard. Just keep a couple of spare single 1st strings, or any that you find are breaking. You get them cheap on ebay, and it only takes 2 minutes to change one string. It really is a small sacrifice, nothing to worry about.
2. Yes, there is a big difference in technical difficulty between say, 'I Will See You Again', and 'Rylynn'. I wouldn`t know about Defour`s stuff, but I`d be willing to bet that the same applies. There are numerous threads on this forum where people discuss this issue. I think the general consensus is the easier ones to start with are, 'All Laid Back And Stuff', 'I Will See you Again', 'Nocturne' and maybe 'She'. Having said that, I went for Drifting because it just happened, that`s the one that inspired and drove me. I went onto 'All Laid Back...', but got bored of it and never finished it. It did, however, introduce me gently to the string slap, which bacame important when learning a lot of his other tunes.
That`s another thing to remember, every one of Andy`s tunes will teach you a new technique or improve your technical ability in some way. EVERY one! That`s why it`s so addictive, you feel like you`re really pushing yourself, but the increase in ability that comes with it is very satisfying.
3.From a personal point of view, I was practicing anything beween 1-5 hours a day, still about an hour a day at least now. Someone else put it well in another thread on here, he said something like... If you practice an hour a day, you will progress well. Anthing more than that and you will progress quite a bit quicker.
I also find that breaking up my sessions helps me learn quicker. I play fo 10-20 mins, then put the guitar down for a similar amount of time before going again. I used to play for like an hour or two on end, but your brain gets tired, so anything over the first 20-30 mins is inefficient use of time. Plus you may end up getting frustrated, having spent an hour on one little section but you can`t get it because you`ve unknowingly become mentally tired. Try to avoid that.
if you were to practice 1 hour a day, you can be a nice solid player in 1-2 year(s)
if you were to practice 2-3 hours a day, you can be a nice solid player in 6-12 months
Patience is the key.
If you`ve not already done so, I`d browse the other sections of this forum. There is some great advice on quite a few of them, from Strings, Nails/picks, Techniques, Harmonics, Posture etc. etc. The list is endless, but it helps no end. Doing the right thing for half an hour is more effective than doing the wrong thing fro 4 or 5 hours
If you`ve any other questions, don`t hesitate. I`ve gained a lot from this place so I`ll help you to the best of my ability, as I`m sure many others will too.
The best bit of advice I can give really is the simplest. Enjoy it.