I want something to use when staying out at a party for my toddler son to sleep until we are ready to leave - should I buy this or the sleeping bag?

I would say this is very similar to a sleeping bag except that it doesn't zip up. And this has a pillow attached and therefore has a place for your toddler to lay his head. I don't think a sleeping bag would. If I were your situation I would absolutely use this.

The tag says to wash front load machine only. Has anyone washed it in a top loader? Was it ok or did it get ruined?

I have washed my son's nap mat in a top loader at least once per week for the past 2 years. I use a normal wash, hot water, and dry it with high heat. I wash the pillow insert each week as well in the same load. The only thing that's deteriorated is the tag. My son loves his nap mat, and so do his teachers. I love the ease and durability.

Can this be personalized?

The material can be embroidered on, unfortunately we do not offer that service.

How compactly can you fold/roll it up? Basically-- how much space would it take up in a suitcase (if you removed the pillow)?

It would still take up quite a bit of space. It's not thin... It's not too thick either but if you roll it up the way they want you to its the width they list and about 16 inches round. It would be smaller if u folded it flat but it would take up the size of a carry on. You wouldn't be able to fit much else. Hope that helps. It's extremely well made. I love it.