Placing space between the turns of a primary coil reduces the inductance which will cause the coil to draw more current and if used in a non-autotuning design will cause a loss of output from detuning the coil. In a standard SSTC with antenna feedback it shouldn't affect tuning, but it will require additional turns on the primary. Solid state coils require a very tightly coupled primary to secondary, by the way. Only high power DRSSTCs and spark gap coils function well with loose coupling.
There isn't really a chart as there are thousands of options. Generally you pick a mosfet by looking for one with a Vds MAX (blocking voltage maximum) >1.25 x your supply voltage and then look for as low of a RdsON (on resistance) as possible. You need to choose one which can handle the peak current safely, which is Id MAX (drain current maximum). Again aim for at least 25% overhead. If you are going over about 500KHz you need to look at the gate capacitance (gate charge) and switching speeds (turn on delay, rise time, turn off delay, fall time) which gets a bit more complex. Smaller numbers for gate capacitance and switching delay & rise/fall times are better.
Also, there is more to a mosfet than its datasheet. IRFP460's have been known to fail for no apparent reason in TC environments. The flipside is they are abundant and cheap. IRFP260s are much hardier and if you are only using 120V mains or less, will work fine and replace the 460s. I'm partial to fairchild's FDL100N50F mosfets as they are real mosters at 500V 100A TO-264 and very robust. I use them in my Harmonic-Output-SSTC, which operates are more than one frequency simultaneously. This punishment would blow 99% of other mosfets, but they run just fine even on semi-small heatsinks. The flipside is they are very expensive at $25 each.
Ohh, and those UCC gate drive chips cost me $4/ea + $8shipping here in the US, so keep that in mind. If you can afford it I recommend ordering at least 4 total, they are VERY static sensitive and require decoupling caps right at them when in a circuit.
I've never tried the 555's pin 5 for audio, but then again I don't use the 555 part of Ward's circuit as it is very poorly designed. It alters pulse width and frequency but the two controls do not operate independantly. Changing one will change the other and the entire range is pretty useless aside from making a loud noise. His 555 subcircuit is an interrupter which operates in the audio frequency range, I think between 200Hz and 1200Hz. For audio modulation via interruption (be it enable pins or a standard interrupter) you need the interuption frequency to be at least 20KHz. The higher the better. An interupter for streamer growth needs to operate between 50Hz and 300Hz as this is the optimum range for growth.
