There are still welds in there - I think I need to see how I get on with the welding to see how accurate I am with it...then if I feel confident enough, i'll drop more of the bolts & weld instead (like the table surface). I do want to make it so that the whole frame can come apart into manageable sections for moving house etc in the future.

Regarding the height adjustment - I don't know is the short answer...I've seen that others do it & it might be useful for me at some stage - but I don't have any examples in mind. In reality I probably don't need that much. I'm also still playing with the overall dimensions a little - so i'll still be tweaking for a while.
The frame at the moment should be a decent height for me to work at - i'm conscious of making it too low & giving myself back issues (which I get from time to time)...more cross bracing can be added at a later date easily enough.