you can skip the thermometer in the boil kettle if you want to save a few bucks. boiling water will always be 212 degrees.
you dont really need a sight glass in the mash tun either, as you will know how much water is going into it to begin with, and the grains will not give you an accurate reading. the level will only tell you how much combined water+grains there are, in gallons- which isnt that useful to know. and you will be constantly cleaning grains out of it which is annoying.
put a temp probe in the HLT and mash tun, and a sight glass on the HLT and boil kettle.