ok well i'm a total flower hoarder so i have a good 500-ish hybrids or something bc i'm psycho, but i think if you're just lining your paths w/ one hybrid on each side, maybe 100-200 (sorry for the wide range haha) will do depending on how think your paths are and how much pathing you do.
honestly, i would recommend just putting down paths first (or doing a rough pathing job just to see where you want to place them eventually) to see how much space they take up + how many hybrids you think you'll need. it's a lot easier to estimate once you see your paths down
Real talk: You can really never have too much flowers and if you find yourself drowning in hybrids, you can always have a giveaway. Then all the flower hoarders like 5cm/s can swarm in and save you.
Like I'm kind of in the drowning stage and I might have to SOS soon.