Microwave Caps

Does anyone know if microwave caps can be used in a tesla tank circuit?  
My father works for an appliance company and has access to some from the 
repair department.  He found out that they are rated at 5000 volts, but 
did not get the capacitance.  If they are usuable, what voltage handling 
would I need?  I'm only using 1 15kv 30 ma neon right now.  Would I need 
15 kv handling, or 30 kv handling for AC use?  

Regarding rotary gaps...  I have been told previously that using a neon 
system with a rotary is not necessary.  I have built a rotary, however, 
from a circular saw blade.  It is not balanced as well as some of the 
other described rotary gaps on this group.  I spin it at up to 3000 rpm, 
controlled by a variac.  I think that if I speed it up to 10000 rpm, as 
described previously, it would explode (no thanks!).  Is 3000 rpm 
sufficient for a neon system?   

Is it safe to use a properly rated variac with a cap start motor?  What 
is the difference between a cap start motor and a regular one anyways?

One more question for anyone out there.. (sorry for all these questions, 
but I need help!) -yes pun intended

I finished up a van de graaff.  It don't work!  I was very dissatisfied 
with these results.  The belt is a real van de graaff belt from Edmund 
Scientific.  I used the ground from my house to self excited the unit (is 
this house ground a problem??).  The dome did ever so slightly charge.  I 
could get really small sparks (2-5 mm).  The problem is that the belt 
kept falling of the spool pulleys.  Any suggestions?

Thanks in advance for any help you can provide!