Tipping

You tip only if they provided exceptional service an went above and beyond.

Here is an article from the knot that is helpful https://www.theknot.com/content/wedding-vendor-tipping-cheat-sheet

It's not tacky at all! That's what my husband and I are doing for our upcoming reception - tipping them later. Obviously not a month later but I am sure we will be too drunk to even think about that at the end of the night. & I also don't want to put that responsibility on anyone else (even though we have a coordinator)

As far as cash app & zelle, I would say that MAJORITY of our vendors preferred those method of payments (bartender, photographer, videographer, DJ, & event decorator)

If you have used a cash app to pay those vendors already, I don't see an issue with it. However its possible your vendors are not set up on a cash app, so I wouldn't want to do anything that would make an extra step for your vendors to get tipped. If there is ZERO effort for your vendors to get money through a Zelle payment (not needed to set up an account, link a bank, etc) then I say it seems appropriate. Plus, as others have mentioned, it allows you to provide an appropriate tip based on the service you receive.

I will caution that for some vendors, it make be more difficult for them to distribute tips to others after the night is over. I could see this being a particular issue with catering where a number of servers or bartenders work an event but don't consistently work the same events all the time. So I might be tempted to do cash for tips you expect to be given to the head of a service operation and distributed among workers, but then use Zelle for services that are more or less rendered by a single person or whose services may not be complete at the end of your wedding day, like your photographer.

Disclaimer: I've never used Zelle, so if it's more "automatic" than something like Venmo or Paypal and part of what I'm saying doesn't make sense, just disregard that point! I just don't think vendors should have to complete an extra step, like setting up an account, or linking a bank to a payment processing system, that would be outside of their normal operations in order to accept a tip from you.