tseng 4000 1mb video card
I would go scsi. so scsi card + hdd + cd drive + zip drive
some soundblaster card. (others here have better opinions in this area than i do)

A 286 is not anywhere near fast enough to utilise the additional speed of a ET4000 card - any basic VGA card will be fine, Cirrus chipset cards are quite common and more than quick enough.

Memory expansion will be quite limited - if you have simm slots expect to be able to use 1 or 4mb, you generally can't use modules any higher than 1mb in density. If you have dip chips then you may be limited to a max of 1mb. You normally don't have support for Expanded memory or the ability to load drivers/utilities high, so memory management/careful setup of your config.sys is also a little more tricky on a 286.

Storage will be the most limiting factor - BIOS options for hard drives on a 286 will be very limited. You may want to look at an add-in card like a Promise eide-max or the XT-IDE project in order to use more modern IDE drives. You could go SCSI, but all of those devices are going to be ancient now as well. (as well as noisy and slow compared to a modern IDE drive or even compact flash module).

I'd reccomend either an 8bit Soundblaster, or a SB16 instead (if you don't have enough 16bit slots, they can be fitted in 8bit slots instead, as long as you don't use their onboard ide/cdrom interfaces). You'll likely want a MT32 device and MPU401 interface card to go along with it, as the MT32 was the de-facto midi standard while the 286 was in it's heyday (eg the Sierra adventure games) - there's not much released later with General midi support that will be playable on a 286.

A 286 can play a surprising amount of classic Dos games - a decent video card coupled with a 16MHz processor is quick enough to play Wolfenstein 3D comfortably.

Here's my 286 build thread, but I went for EGA rather than VGA.
286 Build

There's no reason why you couldn't use a VGA card, but I agree that the ET4000 will never reach its full potential in a 286. If you can get one cheap though, don't let that stop you putting one in, but there's plenty of other options that will be suitable as well.

Apolloboy and I got this system working today, at least for testing.
Among the stuff my dad still had in storage was a 1MB ATi Graphics Ultra VGA card and a IDE/floppy/serial/parallel combo I/O card, so we tested it with those. (that card actually had separate connectors for "regular" and 2.88MB floppy too, which we didn't realize at first -which we later figured out was keeping the 1.44MB drive from working, as we used the wrong port)

Floppy seems to work fine, and we made a DOS 6.22 install to floppy, and it seemed to accept the IDE hard drive we tried (and we put the correct parameters into the BIOS), and it seemed to mount it as C properly too, but when I tried to change to the C directory, it seemed to do so for a second and then skip back to A quickly (leaving the C:\ still on-screen at the previous line).

It might be an issue with the drive being 2.5 GB, or maybe we need to install proper IDE drivers for that specific card rather than relying on the BIOS or default MS-DOS drivers.
If IDE ends up troublesome in general, SCSI should definitely be an option too. I'm pretty sure we have old SCSI drives to spare at fairly low densities, and we should have some ISA SCSI adapters too. (otherwise, those aren't hard to find at weirdstuff -plenty of VLB SCSI cards too)

And as to RAM expansion: this board has no SIPP or SIMM sockets, just DIPP sockets. It's got 1 MB (with pairity) populated as 8 256kx4-bit chips and 4 256kx1-bit parity chips. I think there's space for 8+4 more chips, so 2 MB max.

Anything in particular you're planning on playing on it?

I think he was planning on using it for some more speed-sensitive DOS games, particularly since the turbo switch seems to allow for 8 MHz too (still might not be right for a rare few 4.77 MHz 8088 dependent games -mostly certain PC-booters iirc).

I was personally more curious on just how well a fast 286 could handle some of the late pre-IA32-requiring PC games/apps (like Wolf3D and Wing Commander), and actually finding a 286-20 board (in good shape at that) isn't an easy task either.
Technically, a 286-20 could actually run some things faster than a 386SX-20 due to the longer cycle times for several common 8/16-bit instructions on the 386 (compared to 286), but you'd need a 386-SX system for that comparison.

So far the most intensive game tested was Catacomb Abyss, which was totally playable, but admittedly choppy after being used to seeing it maxed-out on a pentium. 😉