As long as you don't have any pressure on the brake lever, fluid will not spurt out. It will weap out slowly.
Also, you can replace the new bleeder without having to bleed the system. As long as you don't let the resevior empty that is. But you should have a few minutes to do it without worry. However, I would suggest not tightening the bleeder fully until you see fluid coming out the top of the bleeder.
As for putting teflon tape on, there shouldn't be a need. the threads do not seal the bleeder, the end of it does. the end of the bleeder has a tapered end, and the caliper has the mating end at the bottom of the tapped hole. That is where the seal is made, not with the threads. If you have weaping past the threads, the seat may be gulled up. Besides, I don't think teflon tape will hold up to brake fluid, I'm sure it would be eaten away rather quickly.
Replace your bleeder and don't over tighten, and see if the weaping stops. if it doesn't, your seat may be bad and the caliper may have to be replaced.
And no matter what you do, DO NOT press on the lever with the bleeder out. If you do, once the bleeder is released, you will pull in a ton of air into the system. But Im sure you are aware of that, just saying it just in case.