You seem a bit overwhelmed with the cornucopia of options you've been given. I can tell you what worked for me.
My current 90's box is:
Motherboard: PC Partner MVP3BS7 (Via MVP3 Chipset)
CPU: K6-2+ 500
RAM: 256 MB 100 Mhz SDRAM
Graphics: Geforce 2 MX 400
DOS Sound: AWE64 Value (CT 4500)
Win98 Sound: SBLive Value (CT 4780)
Storage: SD to IDE adapter with a 32 GB card
PSU: FSP300-60ATV
Overall, I'm really happy with the system. Between SETMUL and MOSLO, it runs everything from Might & Magic 1 to Quake 3 at playable speeds. Although I'd definitely say it maxes out at Quake 3, and even then there are certain rooms with effects that immediately drop the framerate in half. Like teleporters. The original Unreal ran ok I guess. About 20-30 fps most of the time. It passed for playable back in the day. Battlezone from 1998 ran at a similarly "acceptable" level of performance, slowing down a little with lots of action. Diablo II from 2000 ran, but in D3D I had to turn off the perspective mode and reduce some of the quality to get nice consistent framerates. Sacrifice, also from 2000, had a barely playable framerate just walking around, and was a total slideshow if any fighting began. So I'd consider that unplayable.
Running two sound cards wasn't nearly as hard as I thought it would be. I just reserved a bunch of unused IRQs in the BIOS for Legacy ISA to bump the SBLive out of the range DOS games look for, and then ran UNISOUND to initialize the AWE64. In fact, using the utility EK1M to set the mixer settings for the SBLive, I have it being used as a dumb mixer for the PC Speaker, CD audio and AWE64 is DOS. Then in Windows, it's all SBLive all the time, with the AWE64 totally disabled. I hadn't initially considered going with 2 sound cards, but the SBLive was difficult in enough DOS games that I just bit the bullet and did it. Compatibility aside, a lot of DOS games just didn't perform as smoothly as I thought they should with the SBLive dos driver. With the AWE64 they are now buttery smooth.
If you aren't in a hurry, none of the parts are particularly expensive. I actually see a lot of SS7 motherboards selling in Ukraine and Russia for reasonable prices. If you don't mind waiting a month to get them. That's how I got mine for $15 + shipping. You'll also want to make sure they are K6-2/3+ compatible. The CPU is probably the next most expensive part, probably running around $30 or so. Same goes for the AWE64. And I wouldn't skimp on the PSU either. I picked mine to have a -5V rail. But I don't believe that was strictly necessary. I had a... mishap with a used power supply. I'm never doing that again.
Feel free to PM me if you have any specific questions about my build. It's pretty vanilla so far as 90's time machine builds go.
Win95/DOS 7.1 - P233 MMX (@2.5 x 100 FSB), Diamond Viper V330 AGP, SB16 CT2800
Win98 - K6-2+ 500, GF2 MX, SB AWE 64 CT4500, SBLive CT4780
Win98 - Pentium III 1000, GF2 GTS, SBLive CT4760
WinXP - Athlon 64 3200+, GF 7800 GS, Audigy 2 ZS