Found this OG PS2 at a local Goodwill for $10. How could I pass?

I have taken it completely apart, cleaned it pretty thoroughly (actually pretty clean, all things considered, except the fan), replaced the CMOS battery, and am now waiting for a big Arctic Cooling's thermal pad to replace the original, dusty, rubbery, dry one that was in it. Once I get that (along with a PS2-proprietary display-out to 5-RCA adapter, 5-RCA to HDMI converter, and a new third-party PS2 controller), I'll reassemble it, cross my fingers, and hopes it turns on (and if it doesn't, welp, oh well).
Also, any suggestions as to how to make the most out of an IDE hard drive if I were to put one in there? I mean, either I could go the high-capacity memory card route, have one - maybe two of them for all of my PSX/PS2 needs, or I could get an old, say, 20-40GB IDE HDD and stick it in there, so I could not worry about a little external card, although using an internal IDE HDD would be noisy, hot, and draw more power I would think, so I'm finding it hard to see a reason to plop in an internal hard drive into it.
Oh, and one more question. Are there any significant performance differences between the original fat PS2 models and the later slim ones?