The first thing I do with any new computer is remove all the crapware, trialware and spyware which includes the free trial period of stuff like McAfee.. In the early days of the internet, the antivirus program was critical as any virus would typically render your computer unusable and would for sure disconnect you from the internet.Back then programs like Norton Antivirus or McAfee were huge, but as time went on and the operating systems evolved to become more secure (back when Windows XP and Microsoft stated they would not release the operating kernel to antivirus manufactures), it became necessary for these programs to first DISABLE the build in windows security including the firewall... it is at that point that you have to ask yourself, just how good is a program that first disables the built in security? If some bug/program was able to disable the McAfee or Norton antivirus then it would have free reign on the operating system.. it is at that point, when these programs did this, that I started looking for other antivirus options and as you have now done, choose AVAST as my go to antivirus program. These days there still are viruses but most of the viruses are malware/spyware related where they get in to your system only to retrieve such things like your address book or internet history, but most definitely not to disable your ability to get on the interent.. quite possibly block you from getting to various websites that may help remove said malware, but that is why you should still have antivirus installed on your windows computer.
The problem I have with any antivirus/malware/spyware scanning software is just how much they want to be the be-all-to-end-all program, the one that does everything and that goes with the latest version of AVAST (version 8) where it installs by default the 'software updater'.. as much as this is a good thing, to have a program check to make sure you are up to date with all other software installed, this is something you should already be aware of and/or will be aware of the moment you go to use that program. Having a program constantly monitor the status of other programs only means one thing.. that it is going to be slowing down the efficiency of your computer, adding yet one more running process. The other is the fact that this 'freeware' software does come with a pro element and just like any other free software, they will always promote the pro version by offering you some sort of free-trial and sure enough if you fall for it, when that free trial is up, in order to go back to the free version you will most likely be finding yourself uninstalling the software first and then having to reinstall it.. this is why I also suggest when installing any program, to use the CUSTOM install mode so that during the installation process you are prompted along the way as to where to install, and WHAT to install and you can then choose to only install the main elements of the program. In the case of AVAST, choosing CUSTOM and then once you choose this, DISABLE the items from the Custom section altogether (software updater, browser, cleaner, etc).
Now on to answer your question.. yes, you should leave the windows firewall on and yes, this is absolutely enough protection so long as you have AVAST installed. But what I would also suggest is you visit my website at http://tpsconsulting.com and read the TIPS page on OPTIMIZING your computer. Then go to the SOFTWARE/SUPPORT page and install all the programs from the PINK section as they will help with the ongoing cleaning, removal and maintenance from the malware/spyware that can slow your computer down and basically create issues that you will find very annoying (start up items for example, which can be adjusted through the TOOLS section of CCLEANER).
Basically with CCLEANER and MALWAREBYTES installed, along with AVAST, they can provide pretty much all the safety and security as well as cleaning tools your windows computer should need. Then, if various other issues to crop up, you can turn to some of the other software tools to perform more evasive scans and removal processes.
One other thing I might mention is that even though I am saying to leave the windows firewall on, I do disable the Windows DEFENDER on my Windows 7 and 8 machines, simply because Microsoft has NEVER been very good at detecting malware and if/when they do, it is typically too late and since this only adds yet another set of monitoring processes further slowing down your computer, I turn it off. This is not a very big deal however, since the defender definitions are part of the normal windows updates, if you do decide to leave it on, it should be kept up automatically.. the thing I have noticed however, is that if you do read the Microsoft defender website for windows 8, they make it sound like having this installed and running should provide enough security from the malware/spyware issues when it only gives the user a false sense of security (much like what McAfee and Norton do with their software these days)... since I have on numerous occasions, found that running a full malware scan (using malwarebytes) on a windows defender protected system usually ends up finding numerous items that were not detected by defender. So if you use AVAST as well as CCLEANER and MALWAREBYTES and perform routine scans, you will most likely find that disabling the defender is only going to enhance your performance of your computer.
The other issue is the actual removal of the free/trial ware software. In the case of McAfee you will want to confirm the all-clear by installing the clean up tool which you can find here.
If you have Norton installed or did have it installed, then using the Norton Removal tool found here.
