My own personal order
Mask, fins, snorkel (I refer to them as diver's underwear)
Reg (ease of breathing, comfort and ...peace of mind as to how it has been used, maintained, etc)
Thermal protection (fit, comfort and warmth)
BCD (fit, bulkiness (or lack of if you will be travelling with it) and style (back inflate, wing or traditional...based on your style of diving)).
While good thermal protection may make a dive more enjoyable, a leaky mask or one that has pressure point will definitively ruin one.
If you are on a tight budget (like most of us...we all have to make choices), I would second Netdoc for HOG D1 CW reg and the other individual who suggested HOG/Express Tech set-up. As a matter of fact, I am quite surprised that Netdoc did not make that recommandation (Express Tech). I am pretty sure both items can be acquired for less money than the SP reg you are considering, they will serve you very well and they will last a lifetime.
My own personal single tank set-up...Sherwood SR1 reg and Express tech (upgraded to a 30 lbs donut bladder). I also have a Mares Dragon but now prefer diving backplate and Wing instead.
I purchased my SR1 reg set-up (SR1, Dual Octo (now upgraded to a mares metal Proton Octo) and console for 700.00 brand new) at the annual sale of a major DS in Montreal. It is a sealed reg, breath effortless and has served me very well on deep and cold water dives as well as diving trips down south.