I'm not sure what you mean by the source. It's like the magus was experimenting and got a Discovery, and then confirmed it. The Insight should be appropriate to what the magus was doing in the Magic Realm that season.
No, I don't think so. The magus has gained special insight into the Magic Realm, and gotten a new spell to represent that insight. They shouldn't have to confirm it.
No, the amount of vis they would have gotten determines the level of the spell instead.
You refer here to RoP:M p.28, which again refers for Insight to AM p.8. Right?
Source is a concept from AM p.8 which determines, just what a magus studies to gain a specific Insight. As the magus does not really study to gain an Insight into the magical manipulation of the Magic Realm by RoP:M p.28, it doesn't play a role there.
In the sense of AM p.8, there are no sources to investigate for a season, before you gain RoP:M p.28 Insight. Converting the vis to Insight is sufficient.
By AM p.8f and RoP:M p.28, your Insight allows you to create a specific effect. Creating a specific effect by AM p.8f is a lab project at which you must experiment. RoP:M p.28 does not change this.
Erik Dahl is an author of RoP:M, and apparently interprets the text differently - but I do not understand what he means by 'confirm'. If it is (HoH:TL p.28) stabilizing a process that once led to a Discovery, this is not needed to gain breakthrough points from an effect created after AM p.8f. This difference is very important, as it means that you accumulate a lot less Warping points by following Insights, than by doing HoH:TL p.26ff Original Research.
This is very important, if you need to create the effect for your Insight in the lab. See:
This might hold also for converting vis to an Insight into the magical manipulation of the Magic Realm.
Therefore, the magus has not to expend another season investigating the source of insight and cannot write an insight Lab Text, right?
According to the One Shot quote, the magus should create the effect to obtain the spell, right? and if the effect is successfully created, the magus gains a number of breakthrough points equal to the magnitude of effect (AM, p9). RoP:M does not change it, so you will be able to achieve the Breakthrough adding this points to the Breakthrough points from original research. Right?
He gets the Insight without further investigation, just from the converted vis. So he does not write a lab text during such an investigation, either.
But if he would take the time and write down his experiences, musings and conclusions, he thereby might create a text others could read to gain the same Insight.