Diy: Garland/fireplace Decor Help

I've never done any DIY florals before, so I need some advice for creating a garland. We have a beast of a fireplace as the backdrop for our ceremony and our table at the reception. The mantle sits 9' feet high and it's almost 12' across. The mantle itself is 12" deep. We want to do lanterns on either side of the mantle, our initials (large, it's about 8' across and they're fairly tall), and some greenery. I want to do fake greenery since it will be so high up it won't really be noticeable. But here are my questions...

1) Should I try to do greenery all the way across to fill the space or should I do a splash of greenery right around the letters and that's it?

2) How do people attach greenery or pre-made garlands together to make them look real? Every garland I've looked at has gaps or is very flat. I imagine people stack them on top of each other to fluff them up and I was wondering how people go about doing that?

3) Does this seem like enough for the size of the fireplace? The venue website and Instagram always shows the people who go all out and get thousands of dollars worth of florals and greenery on the fireplace and I'm not willing to spend it on something that's just going to go in the trash after the ceremony but I also don't want it to look weak either.

Bonus question: The letters are paper mache letters.... What color would you paint them? Our colors are plum, pale yellow, and orange... All those feel like it would either ruin the softness of the brick on the fireplace, but I'm worried white won't stand out.

This fireplace is so gorgeous and is initially what made me want this venue and now it's the biggest source of stress! Go figure!

Letters we plan to use on fireplaceFireplaceAnother angle of the fireplace