Phono Newbie

After saving my pennies for quite some time and with much appreciated help from others here, I recently purchased the following: AR 300.2 amp, AR LS17 pre-amp, and Magnepan 3.6 speakers. I have a small collection (about 50) of vinyl from the mid 60's to mid 70's that I would like to listen to. I also have an old Onkyo turntable (circa 1980). I need a phono pre-amp, but am at a loss when I read terminolgy that includes things like 47k cart load, etc. Since my vinyl collection is small, I want to keep my phono/pre investment modest. Where do I start? Is my Onkyo still usable? What should I look for in a phono-pre?
Until you decide to take a jump into vinyl, I would think that your Onkyo should be just fine for playing your 50 records. You will need a new phono cartridge as yours is almost definitely the victim of the ravages of time. Take a look at the Ortofon Blue and Red, they are very nice, inexpensive, cartridges, for a bit less, the Audio Techinca AT95E. For a phono stage, only the fittest has survived. The NAD is a nice entree into the sport, but for a few more bucks you should have a look at the Cambridge 640P.
I second the Cambridge. I have one and if not for my Sutherland, it would be my regular phono pre-amp.
I'm at a crossroads as I'm sure many here have been. I purchased the Cambridge 640P phono-pre as suggested.Whether I use my old LPs or a few new ones loaned to me by a friend, the sound has very little dimension. Also, regardless of whether I set the phono-pre to MM or MC, I have to turn the amp volume way up to get decent sound. Clearly something is wrong and I would imagine the problem lies with the turntable. So now do I invest in a new cartridge? A new turntable? Or just abandon and continue on with CD? Any thoughts?
As Viridian suggested initially, be wary of that old cartridge. If the cartridge has been sitting unused for a decade or more, it's very possible that the cartridge suspension has stiffened to the point that the it is no longer useable. Not only will the sound be bad, you risk damaging your LPs. Viridian's suggestions for a replacement are cost effective possibilities.

If you're think the cartridge is fine, you may have a some short in the connecting cables from cartridge to phono stage or phono stage to preamp that is shorting the signal and reducing the volume. Check your cables and connections carefully to ensure that they are clean, tight and don't have any stray wires touching a ground.

If you can try the phono stage in someone else's system, that will give you confidence it's not a factor (or confirm it's defective).
LP's will always have lower output than CD's therefore you will have to turn the volume up more.