Tele Vue5x Powermate 1.25 inch (1-1/4 in.)

I'm not clear on how to calculate the "25x per inch of aperture of the telescope" with a barlow. If I have an ED80T CF, which Powermate do I need?

do you have these in stock??

Will this work with an Orion XT10?

Does the televue barlow come with only the brass ring or is there a model without the brass ring but instead with a padded point screw version?