The difference on Head, Cabinet and cambo is simple.
Head= Amplifier, no speakers.
Cabinet= Box of speakers, no amplifier.
Combo= Both, usually open back with one or two speakers.
You can get a Peavey Classic 30 for about 300 bucks, not a metal amp but nice cleans and rocking dirty sound, all tube so it has a nice punch and is plenty of loud. As for a pu on you LP bridge, try a Seymour Duncan SH-5b. I use them and found them agood all around pu. Not a lot of distortion but I use a 6505+ Head, so gain is no issue but the SH-5 have a nice fat tone and sound great for muddy bluesy/jazz sound and nice fat metal crunch, and you can find them for 75 bucks new.
I hope this helps.