and welcome to Comodo Forums.
(1) Will I be charged automatically every month, even if I chose not to?Take a look here
at the Terms and Conditions (Section 3.2)
(2) Is there a minimum amount of months that I must sign up for? I.e. Do I have to keep paying for 6 months or so?
Again, look at the link above but this time at Section 3.3.
Also, if you purchase through PayPal, you can always cancel your monthly subscription at any time (even if its for only 1 month).
(3) Do I need this even though I already have an anti-virus and an anti-malware programs?
You definitely DO! Anti-virus, Anti-malware or even Firewalls can "protect" somehow your PC from attacks.
But NONE of them protect the info you submit through Wired/Wireless connections.
If you want your browsing or navigation to be encrypted, TrustConnect service its a MUST HAVE.
(4) Will this slow down my computer? (I have a Windows 7, 64 bit laptop)
Not at all!