Video mixing options for a live event

Hi all.

I've got a live event coming up. All of the media is being run by me in a control booth. This makes it sound grand when in fact it's a sweaty box with a power plug, mini jack to the mixer and a VGA cable to the projector...so not much in the way of control, lol.

This is my first live event of this sort and there will be a mixture of Keynote presentations being given, with people clicking through. It's also for a charity, who have built a hospital in Pakistan, so the job is cost sensitive.

These will be mixed between about 3 videos.

I've been weighing up the pros and cons of managing the media and was thinking of going with 2 options and wondered if anyone could provide feedback.

Option 1. Place all Videos into slides and create one big Keynote presentation with all elements included. No cost option and would seem simplistic to achieve.

Option 2. Get some video mixer software. I've had a look but can't seem to find exactly what I'm after. This would give me more granular control but would most likely be more complicated and costly.

I did consider a 3rd option, getting something like a Roland EX-4 which I've used before, but it's expensive and doesn't still do Full HD.

I'd really appreciate everyone's thoughts and ideas, especially around software which might achieve this.

Option 1. A fast computer, Keynote and properly encoded videos. Don't complicate it.