In order to suggest specific plants, I need to know what part of the country you live in. There are no shade trees it seems. I would take down the two shrubs at the front of the walk, including the purple one. Sorry. You can get the purple back elsewhere. They are overbearing and there's no symmetry. At the right corner of your home, not too close where the roots will damage the foundation or branches at maturity will touch the house, place a medium sized ornamental tree. At front, left corner, behind the mailbox ( you need a bigger, more updated one), maybe 5 feet to the right, place another tree. Pull out all the plants that are along the house and replace with evergreens, box woods? Just depends where you live. I would also pull out the white ground cover near the wall, just on the right, in order to achieve symmetry. I would paint the cream stucco a shade of gray darker than your roof and keep the trim white. Also, a new handrail would help freshen up the entry.

Dwarf marigolds are easy to grow from seeds. Don't put in too many, they may all germinate! However, they do not grow all year. Summer is their favorite time of year. Put in sunny window and cover with saran wrap til they pop.

Yes, you should have a more neutral wall color as it will really let your other purple elements pop more. Stick to purple choices that are easier to replace than a back splash.

Love your style and you've got some beautiful furniture there! A deep aubergine purple velvet on your wingbacks would look stunning. I'd tend to stick to purples in this area to keep it classy. Also, a dark purple would be more practical with kids than a cream. I'd keep the chairs you've got, unless they are really wobbly. Get someone to check them out and give you a quote for repairs and then you'll have a price to work against to see if you can get cheaper. OnePlan is right on the style and yet I don't think they look out of place in the room. I also like the idea of bench seats or if you wanted something really different, you could get a church pew?! I don't think the room has too much dark furniture as it is a large light area. Keep us posted with pics/samples of possible fabrics you find. Also, check out fabric outlet places.