Yes you can rinse the sanding residue offf without worring about rust(try using a "sticky rag" also.)
Yes you can wet sand the primer(the only time you need to worry about corrosion is when it is continuily exposed to weather or it is not dried properly. Try using a squeege it does wonders.)
You can use a BC/CC over laquer without any problems.
Drop the PSI a little and deffinetly thin your mix down to 50/50(50/50 will make a huge difference.)
No problem with the questions bro, better to ask then just assmue and waste all that time and money. Peace-