It's perfectly acceptable to add oil to a hot pan. As a matter of fact, it's preferred.
The oil is key to the searing process as it acts to transmit heat from the pan to the meat more efficiently.
I do not flour meat for stews and braises because the flour can burn.
After searing the three batches of meat, you should deglaze the skillet with some of the liquid that is going into the stew so you can save all the flavor stuck to the bottom of the pan.
Also, if you are using a dutch oven, consider searing the meat there instead. Saves cleaning another pan and the deglazing process.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan