Wedding reception food provider

In my opinion, yes (it would be tacky). It's the couple's responsibility to tip their vendors, and guests should not be involved in tipping

Yes. Gratuity for service is on the couple.

Yes. You're responsible for all tipping.

Yes. Couple is responsible for tipping the caterer. I’ve only ever seen a tip jar/tip QR code for the bar tender at a wedding.

The couple who is paying the catering bill is responsible for all tips. Same for the bartenders. Do not put a jar on display for guests.

Well I think it’s just best to tip your caterer 20 percent in advance and not rely on your guest to provide gratuity. I would say a tip jar for the bartender is appropriate and common. So in addition to tipping him personally we are also having a tip jar. We have also asked guest to tip the valet service as well, in addition to what we are tipping.

The only scenario I see this being seen as normal and not terribly tacky is if you're hiring food trucks or something and they bring in one of their own.