get it. 75 is cheap, even for just the tank. make sure the date on the tank is good. they have to be tested every 5 years. if you buy it, and its out of date, its up to you to pay for the test before anyone will fill it.
i am in the welding supply industry. i sell used steel tanks for 70, that one probably looks like a late 90's to early 2000's. its nice because its aluminum. they are real light.
as far as more gauges...you can ad more, if i am seeing the regulator correctly(can you take more pics), you do not need to use the mainfold mentioned above. the iftting on the right seems to be some sort of burst disk. this can be removed, and you can take a piece of 1/4'' pipe(make sure its high pressure) and take the inlet side out of another regulatir and screw that on. this picture looks like what i am talking about.
notice all regs in a line with pipe connecting to them
again, i cant really say what can be done to that reg without better pics or seeing it in person
hope this helps