It will depend on how many IP adresses your ISP is giving you by default. I'd say that mine give 4 IP's per client. If yours is going the same way, then you should be ok.
You can give it a try, you'll see how many apparels can get to the internet at the same time.
But then again, I would still recommend to get a router right after the modem. This is basic protection and it won't have the limitation on how many things are plugged in at the same time.