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I have been going through the extensions etc that we have on our live site on a test site removing any extensions not required, or we don't think that we require, or can temporarily remove. I have also been doing a lot of reading and video watching regarding this and they all say update the extensions on Joomla 2.5.28 to J3 versions prior to running the upgrade. That is except for the templates unless a J2.5 - J3 version to remove completely.
Now from your response you are saying migrate Joomla first, but I can see this causing an issue when we have J3 rolling and our early version of Jomsocial is still a very early J.2.5 version. We do need to keep the Jomsocial content. I would think that the biggest issue will be within MySql. Can you therefore detail how you consider we should go about this.
Yes you right, that is sound good for the starting :)
The Joomla upgrade issue will be safe, joomla developer already provide the doc for how to upgrading from older version, well, this is not related with Jomsoical, I suggest you also post into Joomla forum.