1) Towel sound like it will keep the bottle warm enough.
2) 2 1/4 tsp of yeast will make your reaction go super fast. Most likely will have to replace in about 1-2 weeks.
3) No bubble counter is fine. You can let it run as is, and feel the pressure in the bottle or observe the buuble output instead. However, if you do decide to make the counter, epoxy glue is what you'll want to use. Other glues don't work very well. Epoxy can be found at target, walmart, home depot in hardware sections for $3.
-John N.