1. To sponsor your mother, you must be making a minimum income of $27,674 which is the LICO (low income cut off) amount required to support two people. LICO amounts are displayed in table 3 below.
http://www.cic.gc.ca/english/information/applications/guides/5196e10.asp2. You can switch jobs during the sponsorship process - but you must continue to meet the LICO minimum while the sponsor application is being processed AND while your mother's application is being processed (i.e. 48 months + processing times at local visa office). If you stop working and go back to school before your mother's application is approved, the application will most likely be refused (note that student loans are not classified as income).
3. If you get any time married during the sponsorship process, you will have to meet LICO for three people to continue sponsoring your mother. LICO for three people is: $34,022.
4. Sponsoring your mother will not affect your citizenship application.