I think your situation is well covered by the old joke:
Patient: It hurts when I move my arm like this.
Doctor: Don't move your arm like that.
Why are your trying to put everything into a solve block? For best results, you want to remove everything possible from the solve blocks.
Even in your first set of equations, you start with a set of equations that explicitly define some values in terms of previously defined values. All of these should be removed from the solve block and replaces with simple assignment statements preceding the block. Simililarly, you have a set at the end that explicitly define some values in terms of previously occuring values. These, too, should be removed from the solve block and replaces with simple assignments following the solve block. Only the middle equations, where variables are defined in terms of each other, should remain in the solve block.
Further, if you can separate your equations into sets that can be solved separately, do so. Only include in a single solve block equations that are actually mutually dependent.
Minerr is inherently a numeric process. Don't expect to ever get useful symbolic results out of minerr.
Don't confuse the symbolic processor with the numeric processor. Mathcad is primarily a numeric processor. The symbolic processor is bolted on as an external facility (Maple) with an interface. Just because the numeric processor will handle 250 equations doesn't mean that the symbolic processor will come anywhere close to that.
While the symbolic processor has some remarkable capabilities, and will quickly solve many seemingly difficult equations, it also has some remarkable blind spots, and will sometimes fail to do very simple things, like eliminate a variable that has an explicit definition in the block. The symbolic processor works best if you keep its input as simple as possible. Adding extraneous or trivial equations to a set can easily confuse the symbolic processor. You also often have to try different formulations -- it is not uncommon for apparently equivalent equations to differ as to their solubility or the form of the solution.
Tom Gutman