Do i need general liability insurance?

Is anything coming from an outside vendor? The cake? If so, then definitely. You don't want a guest getting the run around while they argue over whose fault it is.
More generally, as long as the cost isn't prohibitive I'd do it. I was licenced in P&C for many years and the stories I heard were always overwhelming to get any additional insurance offered.

If we decided to go with the cake the venue can provide then would there be any reason to?

The cake would be covered by the bakery’s insurance. You don’t need liability insurance if it is not on your property and you are not providing food or alcohol.

Probably not. I do recommend it, but I've heard stories where the venue had a 24 hour lapse in coverage and that's when the incident took place. That's way left field, though.

It depends on all your vendors policies. Usually general liability is required by the venue to protect for any damages done to the facility. Also that is why it is beneficial to you, because it would cover any damaged your guests caused to the facilities, etc. as far as food and such vendor policies usually cover this because you contracted them to be responsible for that. I would just make sure all your vendors insurance policies are up to date and up to par. They should provide you with a copy of requested. I am not purchasing liability insirance, just cancellation.

A $1 million GL policy is $65 with Progressive. Now, I am an insurance agent, so I def. got one, but I have seen people be sued by friends, family, you name it. Sometimes, there doesn't even have to be intent to sue, i.e. health insurance company goes after homeowner's policy, etc. For $65 it seems like a no-brainer to me.