Intel 440FX (P6) was the first with AGP yes, NOT the 430FX
P5 (Pentium 1) Designs had the L2 cache integrated into the motherboard and was accessed via the FSB rather then a sort of "back side bus" like the pentium 2's etc and NO P2's didnt have any cache on the motherboard, but the L2 was integrated on the cpu "package", this time directly accessed etc (but at a 1:2 ratio), this was only done because it wasnt cost effective at the time to integrate the cache into the cpu die/package (like the P6/Pentium Pro).
L3 expansion slot? your talking about the "COAST" slots on a P5 based motherboard, right? They dont exist on P6 based motherboards
That AUX power connector, i doubt any system listed here based on the P5's and P6's ever used anywhere near 250w, and you can find a far more modern motherboard even as far as the original Pentium 4 socket 423 with that connector or similar - iv seen them from ASUS (P4T??) and other OEM's - even in Dell's.
Interesting side note i have used a Pentium 1 with 1gb of ram (Gigabyte GA-5AA, 2x512 SDR PC133), and Pentium Pro's with 256mb EDO etc, still got working samples of most Socket 5/7 CPU's (AMD, IBM/Cyrix, IDT, Intel etc) - the last socket shared by everyone!