Let's see if we can get the "antivirus and firewall" bit out-of-the-way, by taking a little closer look at what both these tools do .. and how they apply (or don't) in the
Linux environment.
A
firewall is a tool that filters TCP/IP packets. Mainly it prevents outsiders from connecting to your machine. But a lot depends upon
where in your network each machine is located. Many home networks build a firewall into the router, and it's a good one. If so, you probably have no need for a second one. If you're a coffee-shop maven, a firewall won't help you much... you'd have to use some cryptography-based mechanism like VPN that would identify "good guys"
vs. "bad guys" by something other than their TCP/IP network address.
Antivirus tools are automated tools for "shutting the barn door
after the horse has escaped." They try to identify rogue programs before they have a chance to run ... a Faustian quest since the programs are constantly changing.
Your best solution, instead of a firewall, is to use
login accounts. Which,
on Linux, is the default. You are logged-in normally as a user that is not
allowed to do big, system-wide things. (Windows users, on the other hand, usually are password-free, all-powerful Administrators!

) Whether or not a virus "got in," as soon as it tried to do something nasty ... it would fail.
On Windows, you can make your system much more secure, and save yourself money and hassle, if you:
- Reinstall the system.
- Set up a "Limited User" for yourself. Reserve "Administrator" privileges only for actual ongoing system maintenance. Assign significant passwords to everything.
- Review the permissions on various files. You don't need, don't want, "read/write access to everything."
- Make regular backups of your work into another folder and make that folder read-only even to yourself.
- Remember that rogue-programs aren't clever; they're quite lazy. By making your system even slightly difficult to break into, you drastically reduce the chances of a successful entry. The thief will simply try the (probably-unlocked) house next door.