Personally I don't think that Spyware Doctor is the best antispyware. Nor any others. Anyone making that claim is in marketing or advertising, since in the antispyware world it's pretty much impossible to prove.
But if you're happy with it, OK, keep it.
Without a two way firewall you have no safety net. If something new that is not detected by your AV or AS gets onto the machine, you have nothing to stop it doing its thing. The Windows Firewall is very good at blocking inbound, it has no outbound protection and limited control.
A basic, fairly standard type of setup would be to have an AV, maybe a resident AS, definitely a firewall - preferably two way - and one or more demand scanners/cleaners. Apart from the firewall you are probably OK.
Important to back up your files, pictures etc regularly, too. Anything you wouldn't want to loose.