It is truly idiotic (criminal, frankly) that your plumber used standard fittings for bends (instead of bend supports or large loops), and also that the pipe was not fully insulated! Proper installation standards for recirculation has always called for "long sweep" fittings with recirculation. Insulate the piping as a smart step. Pull those pipe supports, insulate with minimum 3/4" insulation...1" is great if you have economical access to such. Then restrap as per PEX spec of 32" (retired for two years, and hope I remembered correctly!) Low velocity is exactly what you want when running recirculation systems. You appear to have low velocity now, so be happy with that. High velocity causes erosion. We have run lots of giant loops successfully, like you described your house has and also, alternatively successfully used a simple site built manifold with circuit setters or plain lever handle ball valves to tweak the two or three loops. Add an good aquastat or snap on Grundfos aquastat. Multiple pushbutton or motion activated might be a really good option. Gothotwater, ACT D'mand systems are terriffic and deserve your consideration. They have a "thermosensor" built in. They offer wireless, but then there is the battery replacement task adnauseum. Get yourself a bright plumber who has experience.