Those are difficult questions, I'll try my best. It's difficult to say with any great certainty when the next referendum will be in the immediate days after the No vote, Salmond resigning and Cameron saying that it had been settled for a generation, it seemed unlikely that we would see one for 30+ years. Right now however it seems likely that we might have another one within 10 years. In fact, the majority of Scots want another referendum within a decade this includes a lot of No voters. I think now the genie is out of the bottle, it won't go back in unless the UK has some serious reforms to make the union more palpable to a much greater amount of people in Scotland than now.
Everything will be a lot clearer after May, where the SNP are predicted to do quite well. Stuff like whether the SNP have a role helping a Westminister Labour government pass legislation in return for more powers for the Scottish parliament will play a big part. More powers could put the independence issue to rest for a while or it could fan the flame and be the source of the legislation that Scots approve of. I don't know enough about English devolution to comment on it.
The SNP at the moment are surviving by branding themselves as the party that will protect Scotland's interests at Westminister and secure more powers for the Scottish parliament as a huge majority of Scots feel the Smith Commission went anywhere near what was promised. They are also sweeping up Labour voters en mass as many Scots feel Labour has gone too far to the right and seeing Labour team up with the Tories for the referendum campaign, even sharing a stage in some cases, did not sit well with your traditional Scottish Labour voter.
Branding themselves as the party of devolution for the time being is also, perhaps, hugely beneficial for the independence movement, as many in the SNP take what is know as the gradualist approach to independence. Basically meaning, let's make sure almost all legislation, tax setting and tax collection is coming from the Scottish parliament and be so good at governing; that a referendum is almost a formality with very few of the big problems to sort out that caught the SNP off guard in 2014.