A lot will depend on the experience level of the owners, it might be as simple as a willingness to learn and an ability to follow orders.
What types of aquaria have you kept so far?
I think Mahurangi tech do a fish keeping course
you may find 6 legs will be enough but better with 8
are you welding yourself?,
i have always found it better to tack it all together then weld joins in opposite sequence to avoid distorting the stand
Creating a rock pool with wave action.
I have been playing with a bell siphon and a Shub as a rock pool
Bell siphon
wave surge currently through 25mm pipe but will alter this to a wider outlet