You have mostly no chance that the t-stat was stuck close. Many are made to stuck open as a security (for overheating). If you want to put coolant in your heads, you can retreive the small hose from the coolant bottle going to the head and put coolant on it. Many will say its overkill because the system is supposed to evacuate air in it. Your oil leak can be your cam seal where the cam exit the engine to move the warterpump belt. But from what I saw, it can loose a good quantity of oil (spreading all over the engine parts around) without any drop on the ground. Did you unbolt some parts tightening this seal during your repair ? If no, maybe you have to search elsewhere. At the speed of the leak you described, it seems to be a more vital (and pressurized) part of the engine (not a valve cover leak too). To be sure if its the cam seal is leaking : Watch if you have oil under you vanity cover at extreme driver side of it. If its the case, you will have a straight line of oil in the same axe of the waterpump pulley and on the upper intake just beside too. Watch your liquids : Is there oil on coolant ? Is there coolant on oil ?