Well first of all, let's address the cap. What you'll want for a resistor is a 50-ohm 5 watt resistor. They look like this: http://www.maplin.co.uk/images/full/2179i0.jpg
All capacitors will self discharge. The idea is to slowly charge the capacitor and connect it before it discharges to the point that you risk creating big sparks. Long story short: make sure you have the final connection to the cap and the tools ready to secure it as soon as the cap displays that it has reached battery voltage.
As far as the box goes, you need to do a little more research into the driver you want to use. There are many equations free and available on that will ask for certain Thiele-Small parameters (T/S) which you may be able to obtain on audiobahn's web site. You can then take these parameters and plug them into an equation along with the frequency you want to tune the enclosure to and then you will get the port size and length you're asking about.
If math and numbers aren't your thing, then you can download a free program called WinISD which will give you considerable help in designing an appropriate enclosure.
again, google is your friend, and i must stress, excercise caution and planning with your capacitor. fried fingers are no fun.