"How often do you believe the Scottish government should be able..."

As often as the Scottish government decides. If the Scottish people are annoyed enough at frequent calls for a referendum, they can vote their government out. The Westminster set have got every interest in stopping the vote for their own nefarious reasons. I'd also add that a huge amount has changed since the 2014 vote, including brexit (which the Scots didn't want), grinding austerity, the imposition of a completely disreputable charlatan in Downing Street and the blocking of laws that should have been in the gift of Scottish people to decide.

Yep, that isn't how it is. But that's how it should be.

"...should be able to put everything else on hold..."

You mean, like Cameron and Johnson were "able to put everything else on hold" in order to hold a referendum followed by four years of all-consuming toxicity between the UK and our partners in Europe? I doubt that the Sots would manage that, yet I don't hear you complaining.