Reflow oven vs even hot plate
I use an old Sears Kenmore 4-element toaster oven for reflow, with a thermocouple probe into a digital multimeter for temperature monitoring. Heat to 150C to activate the solder paste flux (Kester EP256), heat to 190-195 for 90 seconds for solder reflow, turn off heat and let it cool down slow with the door cracked a little until below 180C, then open the door more. 

We do double sided also, using a couple of bare boards to hold the components off the tray for the 2nd cycle, sometimes with kapton tape if we're worried about them falling off.

We can do two 100mm x 100mm boards at a time, and more if the boards are smaller.