If you want to get closer to the truth of how 'valid' an independent Scotland might be I think you'd do well to look at the Tory/English response to the idea of independence and another referendum. They're not exactly as relaxed about the prospect of Scotland going it alone as you think they might be if Scotland was the net drain on resources some claim. I mean, it's Brexit time! It's all change and brave little UK plc is throwing off all the shackles, those pesky hand-fed Scots want to go it alone, it's the ideal time to get rid of them and keep their massive handouts -right? 
The only facts we can all agree on I guess are that Scotland isn't even a small country in terms of size and population, with two major international cities and their infrastructure already in place. It's impossible to know or predict how tough it would be for Scotland in the transition period and probably a decade afterwards as everything you'll read has been spun one way or the other, plus it would depend on political wrangling to know the terms of an exit deal or whatever - but we do know that Scotland on paper - well there's just no reason why not.
Also, this EU membership thing. I really think that folk south of the border need to turn that one on its head.
It ISN'T so much (for me certainly, and a good few other folk I've spoken to) that people in a large part want independence because they don't want to be 'dragged out' of the EU.
It's just as much because with the UK not being part of the EU any more, suddenly this 'union' becomes (to many, many Scots) something it's really not worth being a part of any more.
Pretty soon the UK will almost certainly be starting off on a hugely long period of financial and social uncertainty. Just one country, not a member state. And moreover, one country which has pretty much nailed its colours to the mast as more right wing, less socialist, pretty unpleasantly reactionary and in thrall to its absolutely disgusting press. I think a lot of Scots feel EU or not, why the hell would they want to now be in an increasingly unequal 'partnership' with a country like this when they don't even get EU membership out of it?! What's the point?! Add the fact that the prime minister of this country is quite frankly a person completely unfit to hold any public office and - well, it's shameful.
The Tory party, I may dislike them extremely but the degree to which they now represent the press, the rich and the charlatans is something else, and a significant part of the UK electorate are just fine with that. They're just fine with having a liar and a crook in charge. That's so shocking. I think we are in for a period where it will only become more and more important to Scots to not be a part of this very broken system any longer whether they are able to rejoin the EU or not.