Pick your size, probably either 24 or 27 inches.
LCD/LED roughly the same, but if you get LED make sure its backlight not sidelight.
IPS are much higher quality color spectrum and the colors 'pop' more but the response time is much worse, meaning when playing game the screen tearing and the ghosting is worse, if you are SLIing I would strongly discourage getting an e-IPS monitor.
LCD/LED response time, you want 2ms, the 5ms are all the same but in truth they are something close to 7-8ms when measured the same way the 2ms response time monitors are. Brightness is personal preference, 300 cd/m2 ive heard is really overpowering in a dark room and can cause some eye strain if sitting two close.
For improved viewing experience put a small led strip on the back of your new monitor(s) the back light gives you light in the room and makes the monitors look all the better.
HP, Dell, Asus, Samsung, all good monitor suppliers. Samsung PX24 inch was the best gaming monitor out there but its hard to find them anymore as they arent produced so you can only find refurbed ones which are still incredible. The dell 2420 is a good monitor but its response is slow. If you want two monitors get 2 24 inch. If you want one large, get a 27 inch with a 2560×1440.