Where can I input expenses for these 4 as a self-employed: 1) room rental for events; 2) workshops / classes I've taken for prof. dev.; 3) commissions on art; 4) taxis

On your Business Schedule - T2125, you can make these entries in the following fields:

1. Event Rentals - Enter as Rent  (Line 8910)

2. Professional Development/Workshops - Enter under Other Expenses (Line 9270)

3. Commissions on Art - Depending on what the art is (and if it is an eligible current or capital expense), add the commissions to the purchase price. CRA has rules regarding the purchase of artwork for your business.

4. Taxis - Enter as Business Travel Expenses - (Line 9200)