We have several flower beds that we would like to remove completely and replace with grass.

How should we go about this?

Use something like Round-up? then Till?

Also if anyone would be interested in bulbs - tulip, iris, or some honeysuckle & other vines or plants-peonies, chinese lanterns, beebalm, lillies, hostas... they can have them for free before we start this project

This is probably not going to be an easy task. I think you really need to dig up/remove the plants that have crowns like the peonies, hostas etc. Using something with glyphosatae i.e. Roundup will knock them back but might not kill them with one treatment. So several sprays may be necessary before the plants are actually killed. To be effective, the plants need to be actively growing, so that means the entire removal process might take the bulk of this growing season. That's why digging and removal might be much faster if your goal is to plant the grass this spring. Even killing the iris would just take care of the foliage and not do anything to remove the rhizomes.