You’ll probably get a better idea if you draw it out with dimensions so you can see what appeals to you. Here’s an idea.

Why faux beams? Are there other visible beams in the home that you're attempting to relate to? What style are you going for?

You have a lovely room, i would not cheapen it with fake beams.

Are you changing the carpet to wood? I would not do beams without that upgrade

Wood flooring and changing the fireplace surround would be better use of your funds.

I’m looking to do one center beam and then two or three diagonal beams

Based on the current location of your light fixtures, this is the best you can do in terms of layout

If you really want beams I will suggest (4) beams - one at each end of the ceiling and (2) in between.

I love beams with a wood floor but not carpet. And I agree with Norwood Architects.. If you must do beams keep it simple. 4 total. One thing to keep in mind is that beam unless painted white will visually bring the ceiling down. The reason beams look so nice in large vast vaulted spaces is that the ceiling is brought lower. You notice it. Prepare yourself you will see the ceiling as a bit lower than how it looks now. If this is your thing go for it.

How thick are you going to do them? The wrong size could present a problem. You want the space balanced.

These below have more than 4 but the space is much larger than your space

The ceiling is much higher

Mountain Contemporary Hideaway · More Info

this one appears closer to your height

Scandi Modern · More Info

Transitional Coastal Cottage | Reverence · More Info

Spanish Mission Residence, historic renovation · More Info

Kitchen with vaulted ceiling · More Info

You should aim for making it look believable. So you need to think in terms of beam sizing and spacing between the beams. We don't know the dimensions of the room but from the photo, safe to say that 2 or 3 beams per side isn't going to even start to approach being believable.

Too small/ too widely spaced will end up looking cheap & silly.

Guidelines here: https://www.azfauxbeams.com/blog/how-far-apart-to-space-faux-wood-beams/

I was going to do a 10x10 smaller beams (diagonal) and then 20 foot 10*12 center beam

It's tough to know for sure but all the examples given--your room is smaller. I think beams would bring the vault down and that defeats the point of the vault. Your room isn't expansive enough to warrant them, thus they won't look needed or real ever.

So if I don’t do beams then how can I spruce up the room? Bc it’s too blank for me.

Is the room currently empty or do you have art and furniture in there now?

With furniture, pillows, rug(s), artwork.

Do you have a pic of the current furniture?