1. The ISA bus itself can't do 100Mbps and no retro OS has anything like the optimized network stack to actually get close to that value anyway - and you're going to bottleneck on CPU anyway with systems where ISA bus is tied to CPU speed (as I suspect given your requirement 3). If you want one regardless, 100Mbps ISA NICs are relatively rare, but if you're prepared to pay, there are IBM-branded cards with Intel chipset located in the US pretty readily available on a well-known auction site. They're not that expensive, but when you add shipping across the Atlantic it's not worth it for me at least.
2. No problem, lots of options.
3. Hmm, not immediately aware of this one. Might be able to test it though.
4. What drivers? If we're talking DOS, you either use huge bloated ODI/NDS stuff (in which case the stack, not the driver, is the memory issue) or tiny packet drivers with software capable of using them (mTCP!). The packet drivers I have used (NE2000, RTL8019, UMC UM8009F, 3C509, AMD PCNet, i82586) tend to be happy to be loaded high in autoexec.bat.

As for your other comments - how do you define "quality"? I can understand ditching most low-end Realtek designs, but NE2000 is inherently just old, not bad quality. And in the ISA domain, 3Com has a very good name, with good driver support and decent performance - plus excellent availability. What exactly don't you like about say a 3C509B-C?

Best supported chipsets? NE2000 (i.e. Nat Semi 8390) first, but it's old and slow. After that probably 3Com's 3C509 & co. Third would be Intel's i82586, as used in their 8/16 cards, which are probably my overall favorite ISA NICs. Only 10MbE, but bulletproof, good support and hassle-free operation in 8b slots if needed. 100MbE ISA is a bit niche, it's been years since I did anything with it and that was Linux, not DOS - so I'm afraid no tips there on support.

The Intel EtherExpress cards are pretty easy to get working. I have one set up in my 286 machine, and it works like a charm.

Another vote for the intel etherexpress cards.

Try to get one with a boot chip preinstalled if you are interested in using XTIDE, as normal Atmel chips didn't work for me when I tried it.

However, I was successful in reprogramming the Intel boot chip with XTIDE (using a TL866II Plus programmer).

Otherwise an NE2000 or one of it's many clones also work, but will have varying levels of performance and difficulty in working with depending on exactly which chip you get.

Edit: what is crazy is that various companies took the very simple/poorly performing NE2000 design and stuffed it on the PCI bus. I'll only admit to using Realtek 8029 cards because they were cheap and worked with BNC based 10Base2 cabling (before ethernet switches were affordable)

NE2000 was more about having universal driver support vs. actual performance. The 3com 3c509 series were also universally supported (even the QNX 1.44MB demo disk supports it) and somewhat better performing. Note that throughput on these machines is pretty terrible. Even my EISA based 3com 3c597 10/100 card in a 486 DX4-100 can't keep up with a 100Mbit network, despite being on a bus fast enough to support it.