pump placement doesn't matter. yes it pushes up to down but also down to up when the water climbs back up :p
The main benefit will be ease of filling the loop since your reservoir is high.
For the temperature sensors it's nice to have them before and after the radiators, so you can play with calculating the heat dissipation of those rads.
Otherwise, putting the temp sensor after the heat source will make the fans respond a tiny bit faster to load, so it's a good place to have it. but it works equally well anywhere else in the loop tbh.
Thank you very much !