Is there a reason why you want a tree planted there? To hide something? Provide shade?

I wouldn't plant anything so close to the house. In fact, I would remove the shrubs that are blocking the window. They look too tall for the space.

You already have a plethora of shrubs, too many too much for my taste. And the ones at the window appear to be too close to the house.

I don’t know the z9 climate so I can’t recommend a specific shrub. If you could find something to fit that red shape exactly - and not grow larger - it would be ok IF 60% of what’s already there is removed. IMO of course.

For best results here indicate geographic location. Otherwise main issue with existing shrub grouping is they are all more or less the same size and shape. And clipped to be that way, have the same amount of space between each. This approach is called "Tombstone Planting" because the effect produced is like that of headstones in a cemetery. In addition the formal specimens in planters at the garage corners do not integrate well with the rest of the layout precisely because they are situated in tall planters instead of planted in the ground. Finally instead of another tall narrow shape where you have put the red lines the deciduous shrub at the right corner of the house should be replaced with an evergreen one that is wider at the bottom than at the top. So that the tallness of the house there is reduced visually by the shrub. With something maybe half the height of your lines being chosen for the corner immediately left of the walk. Something with fragrant flowers, to provide a pleasant greeting as the front door is approached.

I’m in South TX USA. The shrub style is very common over here - it’s everywhere. However, I certainly appreciate the lack of interest they bring.

Regarding the space in Red, I was thinking of an evergreen; maybe an Italian cypress (tall, slender) to bring balance on that side of the house due to the evergreen spiral junipers on the right showing at garage entry.

Maybe I’m overthinking, though. Certainly appreciate the opinions.

Italian cypress will never fit there unless you look for just about the most dwarf of the cultivars. And tallness of house - particularly that part of the house specifically - would be emphasized unattractively by a cigar shaped shrub right there in the center.

How many different plant species should I plant in the bed for an optimal look?

It really depends on what appeals to you and how much maintenance you are prepared to do. If you want something more formal, there's nothing wrong with a hedge made of the same plant (like drift roses in the same color, or boxwood, or Texas sage).

Or, you can have a mixed border with small shrubs in the back and flowering perennials/annuals/bulbs in the front, but they require regular maintenance throughout the year.

Whatever you decide, please don't plant too close to the house, and take into account the mature size of your plants. You should have 2-3 feet of space left between your shrubs and the wall once they are fully grown. It takes patience to live with all this extra space in the beginning, but it's an investment that pays off.

Many now take handhelds to garden centers and look plants up on them that catch their interest. So that the information they get about them while considering purchases is not limited to labels and signs present at the outlet.

A dwarf crepe Myrtle would look good there. It will add some color to your landscape. Plant it at least 4-5 feet from your house.