I'm sorry to hear you're experiencing some technical issues that are slowing you down.
There are a lot of things listed here, but I'd like to get someone to help you get to the bottom of them.
Please email me privately with your updated contact information, and I'll get the right people in touch with you promptly.
Territory Technical Manager, South US
Thomas, I partially sympathise because I've been in situations where crashing, fickle behavior and broken relations have slowed me down and stressed me out.
On the other hand, I know from first hand knowledge that the frequency of these errors derives from three things: machine configuration, file access and inaccurate expectations.
For the first issue, buy a computer from a quality vendor with a 64bit professional OS, a good ammount of RAM and a certified video card-and then immediately wipe it and reload the OS because those factory images are crud. Use a virus scanner tested for compatibility and stay away from system ghosting, raid 1, employee monitoring and registry optimizing applications. Use the certified video card drivers and disable the nvidia and ATI window management tools.
Second, the safest course of action is to use a PDM system that provides local file access. If you move files onto the network, then it's on you to make sure there is enough bandwidth for SolidWorks frequent, loading and reloading of data from those files. One network collision can cause SolidWorks to throw an access control list error and bring about the dreaded 'failed to save' message.
Finaly, solidworks loses relationships (mates and geometry relations) when model topology changes and when projected and intersection curves change type (ie from circle too ellipse or from 2 point spline to parabola). On Edge relations are pretty robust as long as the angle between the sketch plane and the object you're converting doesn't change. Intersection curve relations are very touchy and can't be repaired, once broken. For that reason, use intersection curves very sparingly and avoid adding sketch relations to their endponits, instead using pierce relations to the edges that bound the intersected surface and don't trim these curves to other sketch geometry if you can avoid it.
With mates, the main reasons they'll fail on rebuild are flexible subassemblies and limit mates whose degrees of freedom produce unsolveable relations. In these cases, suppressing and unsuppressing the mates usually puts them to rights. Sometimes just doing another rebuild fixes these errors-especially when multiple assembly configurations are involved. In cases where mate references go missing, the cause for this is usually failure to take ownership of a file before editing it and failure to check into the vault a modified referenced document.
That's not going to eliminate all of the issues, but getting a handle on those factors usually makes them rare occurences.