If You Use Avast and Malwareebytes Paid version or Superantispyware Paid version…One or the other You have the best in protection …So in my opinion you don’t need anything else because Avast has spyware protection also…
If it was my choice I would get Malwarebytes Paid version or SAS Paid and get the Full Avast Paid version with their Firewall…
Getting Sandboxie is definitely a good idea, will take quite some time even for the full sandbox in paid Avast versions to get as mature as SBIE. As for MBAM/SAS - I am using both on-demand only (the free versions). They are both excellent but I do not feel the need to pay for the realtime protections, seems a bit of overkill w/ Avast to me.