Yes to the rtd, they will give you finer resolution and most likely better accuracy than a k or j type thermocouple.
As for the element, I suggest a straight smooth stainless one like this
You fit it into a tube, where the gap between the wall of the tube and the sides of the element is as small as you can make it, while still allowing room for grain chunks etc to go past... A few mm max. Then the actual volume of liquid that the unit can hold is quite small - which in turn means that the liquid that flows through it, does so quickly, going past the element at a high "surface" speed. Thus it picks up and takes away the elements heat very quickly, stopping the surface of the element ever getting very hot, and also the mechanical action of the fast flowing liquid, tends to scrub off any build up of protein matter that might tend to occur as temperature increases.
These sorts of elements are great, assuming you are smart enough to make your unit easy and quick to pull apart... They wipe clean with a rag in seconds with no curves nooks and crannies you have to get into with a scrubber.
Not recommending those particular units mind you... Just that one in that style is what I consider to be the ideal.
TB