It should be straightforward to remove MSE by going into Control Panel and locating MSE in Programmes & Features...clicking onto it and clicking uninstall.
If you do have difficulties, please post again and say what operating System you have (Windows Vista, W7 or whatever.)
Answers to your questions:-
1. (a) Not normally.
(b) Download installation file for Avast and Run after removal of MSE.
2. (a) A single programme.
(b) Click the following :-
http://www.malwarebytes.org/
Hans.