For e-Kettles, the elements are generally located as low as possible to avoid risk of dry exposure at any point, avoid interference with stirring or chillers, and to sit under false bottoms in BK/MLT units. Since the elements require some sort of external mount (usually a basic junction box), they are often placed near the rear but not at the back (usually want to be able to push the kettle against a wall without that interference)...45-degrees from the center-back point is just about perfect. This also allows placement from both sides without conflict if you intend to install 2 elements.
Thermowells are usually located about mid-height, in the front, and far enough from any heat sources to get a good reading.
I've also noticed that my brew stand is starting to rust in spots. Thought it was SS coated but was curious whether one could "re-paint" it with something durable that would fix the blemishes and prevent scratches.
There really isn't any cheap-and-easy way to fix rust under an S.S. surface coating without sandblasting and re-coating with S.S. and then re-passivating it. Construction companies (I used to be a design engineer) working with steel often use a zinc-based spray to anodize steel to prevent rusting. If you know anyone who currently works with cold-formed steel (also referred to as CFS or "rolled steel"), their shop probably has a case of spraycans sitting in a closet...every time they cut or ding the steel, the location needs to be sprayed or the steel will oxidize and rust. If you live near a coastline, boat/ship repair shops often have the spray on hand as well, as it also help protect from rust caused by saltwater.