Microsoft's recommended maximum limit for a peer-to-peer is 10, so you would be right at their limit. Keep in mind that it is only a recommendation, and does not mean that as soon as you add PC #11 that your network crashes.
The two biggest issues in a Win98 p2p are browsing, and printing to shared printers. Browsing problems are virtually eliminated if NetBEUI is used as the protocol. However, should you desire to use TCP/IP instead (like for Internet sharing), there is something you can do to reduce browsing problems: Use the one PC that is turned on the most as your master browser(first on during the day, last off at night). Disable master browser capability on all other PCs. By default, master browser capability is enabled automatically with file and print sharing. Disable it under the other PCs on the network. This can be done under File and Print Sharing -> Properties.
As far as printing is concerned, I would limit the number of PCs that can share the same printer. Once a PC prints to a shared printer, it establishes a "connection". That connection remains until reboot, even if a PC is not actually printing to the shared printer. If too many PCs establish a connection to the PC that has a shared printer, some will not print. I have actually seen a problem with as few as 4 PCs connected to a shared printer. NT workstation has a limit of 10 concurrent connections. I have never seen any documentation on the limt for 98.