If your building a retaining wall over 1mtr high in brisbane , you will need an enginner to design it, he will take in consideration of the soil type for how deep to make the foundation, and also how much load is on the wall, if any load bearing surcharges are present like vehicles passing ect. Generally block walls will need a toe in the foundation that sticks out from the wall the higher the wall the larger the toe, the closer the steel risers are and thicker they get. The wall will need to be corefilled with cement usually 25mpa if its over 1mtr high, There will need to a sealant painted behind the wall and gravel backfill and a aggpipe drain, It is very important that the drain functions properly, meaning has fall and drains away to a suitable location or into the stormwater drain. We build alot of these walls and timber ones too, if you go to the link you will see heaps of photos under retaining walls brisbane . Here is a link that might be useful: http://www.cpricelandscapes.com

You have been given so many really great suggestions that I don't think I could think of any that are better or more helpful. I did however want to address the "ugly" wall. It is possible to colorize your wall with what is generally known as "white washing" but by adding a cement additive you can tint it any color you would like. It's very simple really. You would need a bag of white portland cement, a bag of white hydrated lime and the colorant powder of your choice. Mix the portland and lime 3 to 1 and add water so it's a milk consistency then add the colorant until you get the color you like. Measure the colorant as you add it so subsequent batches will be mixed to the same color depth. Brush it on with a paint brush. The painting goes faster than you would think by sort of swishing the brush in all directions to fill all the little crevices, You have about 30 minutes or so to work the cement mixture but if it starts to stiffen just add more water and mix well again and finish up. I did this on my very old cement stucco house this past summer and it is the brightest shiny white you could ever imagine. It looks beautiful with freshly painted trim. Anyway this will work on anything with cement like texture (bricks too) and because of the added portland cement it will not wash away like a simple lime only solution will eventually do. You could even do a really bright color like red or deep blue if you wanted to and consider it an art wall if you wanted. Just something to consider in addition to plants. Any left over materials can be mixed with sand added to make stepping stones or cement planting containers etc. Good luck!

"The holes made to raise the concrete are ugly and the patches are very visible." In my opinion, this is to be expected and is unavoidable. Complete replacement was your only alternative. If your contractor had gotten in before the city, it is likely things would have turned out better. No suggestions about the other issues except to see what he proposes. .

1 - from a design standpoint it's easier to do them both of the same material. Making two different materials 14 ft apart look good isn't easy 2 - to tier or not to tier depends on that specific site and project. Keep in mind that if they're close to each other, two shorter walls are essentially acting as one taller wall. I'm currently redesigning a wall that was improperly built that way in July. I'm redesigning it because it's already failing and the center is leaning 15" out of plumb. Just because someone can stack blocks doesn't mean they can design a wall. 3 - the walkway *can* go up against the wall, but that generally isn't my preference 4 - six of one/half dozen of the other. If you're doing straight runs and no curves, poured might end up cheaper, but it depends. 5 - ehhhhh. The "stone look" walls aren't ever all that convincing. Rosetta probably has the best, but it's also a massive wall system. Where are you in VA that you have Unilock as an option? As far as I knew it's hard to get here. Wall blocks like Anchor or Keystone are almost bulletproof but they're nowhere near "natural" looking. At best they look like a Walmart parking lot built in the 2000s vs one built in the 90s. 6 - There are a couple of quality tiers among the block companies. I would say to let your installer help guide you (assuming they've done a fair number of walls). Some manufacturers are known for slightly less strict tolerances. A block being 1/8" out of square isn't a huge deal when there's a mortar bed. But with segmental walls, where you're stacking one right on the other, that means potentially grinding down every single block to keep the wall level. 7 - A standard timber wall is fine. The metal and timber one, I wouldn't touch without an engineered drawing because it sounds like what's keeping the wall straight is 100% the steel beams. 8 - work with a designer who is product neutral. You want the design that's right for your site, and then we start looking at which product gets that done the best. 9 - look for someone with a deep portfolio. There's a lot of "sure we can give that a shot" out there. This doesn't sound like something that should be someone's first decent sized wall project.