What climate zone are you in or where are you located? Can you take a photo that shows the entire front yard? I can't tell where you park or how guests walk to your front door. If you search Houzz for 'entrance gardens' you will see many examples of homes with wide paths leading from the street to the front door. Do you like to garden? You have a lovely house and would not want to hide any of the porch area so keep the plantings around the porch low. You can plant some taller plants at the base of each post but these should also stay low and not get higher than 3' to 4'. It looks like the garage may be in the back of the house with a fence along the driveway. You could have low growing roses along the fence and flower beds at the front of the house if you like to garden. Location and more pictures would help us to give suggestions for the garden.

Perhaps a colored door if you paint the home grey. Maybe Red? You could simulate a color change on door by hanging something over the door that is the color like a tablecloth or piece of fabric. If you search houzz for" grey homes", you can see what others have done. My home is painted Cape Cod Grey with white trim and it has been very easy to live with for years. I have a dark grey roof.

I agree with you the pillars are unfortunate. The replacement tiles will stand out no matter how close they come to matching so you're better off making sure they are clearly different so the gray one is better. Putting busy mosaic tiles could look nice but will interrupt the flow between rooms which I'm guessing is your problem with the columns in the first place. You will need to create a dextrous solution to tying into the 2x4 wall on the left side but I think it can be done tastefully- maybe beveling it back once you get past he end of that wall.

Wow! What a beautiful home :-) It's got lovely clean lines, but these can also look a bit stark, can't they? Have you considered Espalier or something similar against the walls between the garage doors, etc.? That would add some softness and colour (as well as fresh fruit!). For the front garden, you've really got a lot of choice for such a lovely aspect. If you were after a more 'finished' look, then perhaps consider a front (picket) fence with smaller natives and a bigger grevillea or similar as a feature. For privacy, perhaps a hedge of lillypilly. Or for a more formal look, landscape with sandstone to create tiered beds and plant out with smaller natives, lavender a herb garden or a mixture of all three. Enjoy!