No, 3Dfx isn’t supported, because there’s no Glide wrapper for Android. You can software emulate 3Dfx, but that’s terribly slow, much slower than SVGA actually.
HDD images can be up tp 2 GB, that’s a Win95 restriction. Win98 does suport larger sizes, but it’s buggy af in Dosbox in general. You can always try, though. 🙂