I put together a Windows 98SE system with some old spare parts a few months ago, mainly for playing old games on.
I found some useful threads on msfn.org Unfortunately that site seems to be down at the moment, so here is a snapshot from archive.org which should answer most of your questions regarding compatible hardware, limits and in some cases workarounds.
I did also manage to set up wireless networking within it, but it was not easy, and I could not get it to work correctly with DHCP (static IP assignment worked, however). I posted a thread on it here. Bear in mind that Windows 98 has no built in support for wireless networking, so you have to use third party software, and any modern hardware is unlikely to come with software and drivers for Windows 98. I used an old (circa 2006) PCI wireless card which did come with Windows 98 compatible software.