Jared, sorry for taking so long to reply,
Firstly, I don't know what you mechanical background or ability is. I'll assume it to be middle-of-the-road and we can adjust to suit you as we go.
We might start by discussing the drive starting at the engine and following the belt back to the drives themselves.
All good at the engine judging from the photo. The drive belt should be in the top pulley groove - and it is. Did you assemble the pulley onto the engine or was it already there when you bought the machine? If it was already there, I'd put a spanner on the bolt that secures it and just confirm it's tight and not just sitting there loose. There should be a guard mounted around the cutter belt at this pulley. Don't worry about this for the moment. The cutter belt needs to go on first and I can see the guard in you collection of bits.
Moving to the idler pulleys, I'm wondering if you've got the correct pullies fitted. The photos aren't too clear but they look to be too large in diameter and the belt looks like it might be rubbing the steering shaft? These pullies should be flat and not 'v' shaped in the sheave. I think the two new looking pullies in your photos are the ones you need.
Photo below shows the pullies you need and show the flat groove that the back of the belt rides on. (Note the bracket in my photo is normally welded to the machine- I removed it with an angle grinder
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