In electronic circuit the voltage rating of caps should be at least 25% more than the max voltage of the circuit. so 50 volts is fine
The schematic posted is the heart of the circuit, you can see that is has 2 oshilators.
when I designed the PCB, I added a 3rd oshilator.
all 3 oshilators are identical,
Here is the schematic with the 3 oshilators.
now you don't need to assemble all 3.
Now the IRF510 is no good, it will burn up on you very fast.
I like the IRF640, or FCPF11N60, this one is even better, Higher voltage, it will handle higher EMF.
now about the other little transistors, yes any small signal switching transistors will do. I usualy get the ones from radio shack, they have a box of variety of PNPs and NPNs 276-1604 and 276-1617
Resisitors, you can use 1/4 watt. I'm building mine using 1/8 watt, but it is the 1st time I'm building with 1/8. so not sure how well will work. so untill I report back, Use 1/4. those I know it works well.
Pots, well, here it is your choice, just get 100Ks and 10Ks. I have replaced a 100K with 50K, it works fine but that Freq range is not as wide.