diy Flower Swag

Example of what I will make.

I am wanting to make my own flower arrangement for my arch, bouquet, centerpieces. I am using artificial flowers. I have found many tutorials on how to make arrangements with REAL flowers so I come here to today for fake flower advice. Do I use any foam block to stick the flowers in? A specific size that I need? How do I make sure they're secure together and how do I secure to the arch? Any and all advice welcome. I am not open to purchasing pre-made because I procrastinated and it won't be here in time / I really want to unleash my inner creative monster.

Thank you!