Congrats on choosing McMaster!
Commuting can be a hassle, but a lot of students do it to save money so that they don't have to live in an off-campus house closer to the university. After trying commuting for your first year, decide if it's something you want to continue doing, or you can always look into renting a house with friends that you build relationships with in your first year.
The MARC building is not on the main McMaster campus, it's a few minutes down Main Street, at Longwood road.
If you're coming off the highway, it's actually really convenient to get to the MARC building since it's right off the highway.
Here is a CAMPUS MAP:
And check this out for help with building acronyms for the main campus: