Dave, one of the tools we recommend not to run without supervision is Combofix, all systems and infections are different and what this program can fix on one system can damage another.
As far as Malwarebytes, you have the free version, you can upgrade to the Pro version for around $20 or so, its just a one time fee and you get the license for it. What the Pro version has that the free version does not is a Protection Moduale, what this will do is that if you should wander into a bad website you will get a PAGE NOT FOUND and them a pop up from MBAM that it blocked a potentially bad site, I have this on all my systems and cant live without it, but to upgrade is totally your call.
Correct about the firewall, the windows firewall blocks just incoming , third party firewalls block both incoming and outgoing.
Free Firewalls, like AV, you just need one. Also wanted to point out depending on your router if you use one, most have a built in firewall, you would have to check if yours does or not. You can have one Software and One hardware firewall with no problems
If you are into Physical Security , maybe you can help me get thru the darned Airport next time I fly
Hope this helps and answers your questions, by the way when you run the clean up with OTL it will not remove MBAM and ATF Cleaner, you can keep them both, use them