1) there is no way to thinken the ink, thin it down-yes, but not thicken it.
there is: when i was in school we had a big tub of something used to thicken our inks. granted we weren't using speedball but i used to buy speedball all the time instead of using the schools inks and i think i remember a professor or seeing someone mix it with speedball.
i am wary of this yudu thing. maybe it's because i learned to screen print using a traditional exposure unit, screens ect. i don't like the how you expose screens with those sheets and the ink costs to much (you can get a big thing of speedball for about the same price) and screens aren't that expensive (hint: cover your wood screen in duct tape - it keeps it from getting warped when you wash it out)
i dunno i think if your gonna get a home printing kit get a gocco!