I see no problem in suggesting other AV's as opposed to the OP's choice as long as there is relevant information provided that doesn't simply involve personal opinion such as: Its free/Its good because I use etc.
My only suggestion to OP is:
Swap MBAM Pro from Real Time to On demand Scanner (disable Real Time protection).
Reason being:
*More resources used
*avast! Web Protection is well known to be good, so it will only delay your system when both avast! and MBAM kick in detecting the same infection.
Considering this:
Computer literacy skills: Basic
PC security risk to infections: Medium
How often do you get infections: Occasionally
You can set a weekly scan on MBAM just to be on the safe side.
Other than that, just ensure you are aware of your browsing habits
PS:
Not sure if Sandboxie for the user would be appropriate without proper guidance or a guide.