ok, the 4 speeds won't damage the motor...it's a different winding & well, they built it that way. can't speak for the brand but don't get sucked in by all the hype of 1 brand over another (everybody's trying to sell their own stuff). it's the same w/nutes, too much hype. on size of opening the inlet should be just wee bit smaller than the outlet so as to create what's called negative pressure. just set up the tent, fan, filter. turn it on & watch the tent sides pull in. adjust the inlet till it's barely pulling the sides in & u're set. (close up the tent 1st, of course) u prolly won't need a duct on the inlet (inlet should be one of the flaps near the bottom, as hot air rises). i use the cheapie duct fans from lowe's, about $20/25 & replace every year when i replace the carbon filter. they advertise they last up to 18 mos. the key words are 'up to', so i never take a chance. this is assuming u plan to grow all year round. remember rule #1) NEVER TELL ANYONE THAT U GROW. if u want to show off u're grow....do it here. u should be set.....good luck!