No, it is not necessary to have it completely opaque. It is likely that one of your acetate prints will be enough, and two will just make it even easier. I used to use only one sheet of very poor printed laser transparency, and it worked. I just needed to get the exposure time juuuust right. With two sheets, it works like a charm.
All you have to think about is that the photons of light that hit your emulsion is what turns it from gooey water-soluble emulsion to hard emulsion. What you're trying to do is get MORE light hitting the parts of the emulsion that you want to get less water soluble, so that when you wash it out, only the bits you want to wash out actually do. Your sheets will be perfect, as they will block out _enough_ light so as not to make the emulsion hard.
about the exposure.. i have a beginner speed ball kit which gives a graph that show time-wattage-distance.
problem is i have a 250wat lightbulb, but the lamp i have it in has a sticker that says max 100w. i turn it on and it seems fine. problem is i dont know if its 250w or 100w that its running at.
Your light bulb is running at whatever power it is rated at. Ie: your 250W lightbulb is consuming 250W of power, putting out most of that in light/heat. The "100W max" refers to a reccommended power threshold you should not exceed unless you want to burn out the fixture.
In simple terms, every electical device is rated for a certain amount of current to flow through it. If you're on 110V power, and it's reccomending 100W as a power limit, its probably been designed to run at no more than 1A. You're running a 250W lightbulb through it, and that's 2.5 times the amount of current than it is designed for.
Now, as an engineer, I must admit that in general, components can handle a far greater load than the sticker usually says. the "100W" business is so that when your 250W lightbulb burns out the fitting and either a) leaves you without a lamp, or b) leaves you with a burnt-down house, the company that sold you the fitting can say - "look, it's got a sticker saying 100W max, he's running a 250W lightbulb, his own damn fault".
Be aware that running a device at 2.5 times the reccommended load will create higher temperatures than the fitting was designed to run at. As for answering your exposure question, yes - it's running at 250W.
If you are using the speedball kit with the diazo emulsion that comes with the remover (i.e. **** Blick), I used the same thing once, exposed with a 150 watt clear bulb at about 18-20" for 55 minutes and it worked pretty well.
I dont know what type of printer you have (or any at all), but I have used laser transparencies from work that weren't nearly as opaque as i expected and they worked well for the speedball. I currently use Officemax inkjet transparencies with a cheapass Lexmark printer, and it works fine for exposing QTX. Granted, I havent ventured into halftones just yet...
Confused about my printed positive 
