Need advise - adding to exiting Gravity System

CJRS

Adding to exisitng gravity system...has circ pump on the return side and therefore no control valve on supply to restrict residual hot water after burner shuts off. 1920's house, wood balloon framing, wood sheathing stucco exterior and plaster wall interior has been since been (blow-in type) well insulated in walls and attic clg. I installed new thermo windows (the best) by Marvin. House is now considered well insualted yet had no heat calc. done since then. Existing old column type house rads average 50-55 BTUH per sf floor area. and it's old oil burner boiler converted to gas-fired.
I have replaced one 10,200 BTUH col. rad with 12'baseray rated at 7,000 BTUH in my Dining room and I still have plenty heat. (btw the baseray equates to approx 38 BTUH/sf of floor area) So I am proceeding to add baseray in other unheated areas of the house based on this new formulation of not less than 40 BTUH per sf and not greater than 50-55 based on the deadman formulation apparently used on this old house. Although I realize I may still be oversizing my rads a bit...I too, am not sizing my system too far from its original designers. If anything, I am hoping that the larger capacity of the new rads will hold heat longer after burner shut off and be closer balanced to the capacity of the older rads I am not replacing.
All this makes common sense in my mind but I would like to know if I'm askign for trouble based on a professionals opinion. Thats my first question. The second is to better understand why I have a circ pump on the return side vs on a supply side. I purchased the house this way and it seems to work fine with the old gravity sytem and unlike a circ on the supply side, doesn't seem to have off-balanced the output of the rads. I reside in the central Virginia area and my average gas bill per month does not exceed $200 which includes gas cooking, hot water and the boiler. I am not complaining, this seems real good for a 1,804 sf.ft. home. My third question is that I recently purchased a digital stat vs. the existing mercury tube that was on the wall. I recently changed the location from an exterior walled Living Room which had a fireplace affecting the stat. I moved the stat to an inner hall near the stairwell to the second floor. Now the outer perimeter rooms cool to approx 3-4 degrees diff. before the stat lowers enough to call for heat. How can I compensate for the difference or is there a better recommended location for the stat. (the stat is a common store-bought Honeywell which has pre-set 1 degree compensator for hw gravity systems) Professional comments concerning the above will certainly be appreciated.