I'm mainly trying to figure out what model it is
Surefire Millennium 6 Volt. The Model numbers are a code denoting voltage, mount (ARMS throw lever or dual thumb screw) and tail switch. I can't remember which number place equates to which feature.
so I can buy replacement bulbs (or maybe convert it to LED if that's possible?)and batteries etc.
Batteries are a pair of CR123 primary lithiums. If you use a pair if rechargeables you'll blow the bulb. Bulbs are Surefire P60 or P61 lamp reflector assembly. Your light has the LU60 collar with Z32 shock isolated head.
As I previously noted, the internal diameter of the LU60 is too small for the aftermarket P60 LED assemblies.
You could use Surefire KX4, which is a full head assembly LED conversion. The KX4 would let you use CR213 Lithium primary batteries or a pair of protected LFP chemistry RCR123 batteries. A pair of 16340 (same physical size) batteries of IC or IMR chemistry would put out too much voltage since they come off the charger at 4.2V each. However, with the KX4, you could use a single IC or IMR 17670 battery which is a single cell that's essentially the same size as a pair of R/CR123 batteries. Output would be reduced slightly because of the lower voltage, but the higher capacity would increase overall run time.
Alternately, you could buy a Surefire LU10 collar and use the factory KX9 LED head, or use the old style Z46 bezel (head). With the Z46 you could use the higher output MN series incan lamps, or remove the reflector and replace with a D36 LED/reflector module from Customlites or another maker. With either setup on the LU10 collar you could use three CR123 batteries, three LFP chemistry protected RCR123 batteries, or a pair of 17500 size 4.2V IC or IMR chemistry batteries.
Also it has a push button on/off switch but it looks like it's also got a plug for a remote pressure switch, so I'm wondering what kind of switch might work with it.
Surefire SR or ST pressure switch. Both styles are available with cords from 2 inches to 9+ inches (ex. SR09, ST02).