^Not a bad idea if you just want to have a computer to use. I would suggest locking down some aspects of the mac as apple takes a rather soft stance on many security aspects. Not a definitive list, but a couple things to do.
1. Lock down the bios and single user mode. Never a good thing when someone can boot into the admin user in a few seconds by holding down a key.
2. Disable ssh servers and other non-essential servers, this will reduce the possibility of a remote attack.
Mac's security is ok, and no worse certainly than windows. I really enjoy my mac laptop, and have never had an issue with it. Fewer viruses/malware are written for mac, so its safer in that aspect as well.