The best pry bar model that I know of for lifting concrete slabs is "big" (as in, the bigger, the better). Use a block of wood or something else that's large, to distribute the weight on the ground, for your pivot. You'll likely have to dig out one, if not two sides to pry and maneuver these blocks. Avoid putting too much pressure on a single point, since that can cause the paver to crack.
For the level, away from the house is good if this is draining against the foundation. You don't need much, but keep it consistent by using a level and measuring the rise over the run.
When resetting the paver, don't just build up one edge. That would leave an air gap in the middle that can result in cracking. Don't disturb the ground below the paver other than to remove any high spots, you don't want it to settle after you're done. Just add stone dust to make a level surface. Then replace the paver, wiggle it a little to work the stone dust into a tight contact, and replace any ground that you dug out from the sides.
For weeds, I'd ask over on the Gardening Stack Exchange, but they make lots of weed killers. You can also place a barrier in the ground, or just go with hand pulling. I've also seen suggestions to mix some cement and sand, brush it dry into all the cracks, and spray it with a light mist of water, but that would make any future repairs very difficult.
You need to understand the properties of the materials you're planning to use.
Rammed earth is earth, chalk, lime and gravel, mixed into the right consistency and proportions for strength and longevity. It's then rammed into a form work to form a solid mass.
As it is earth, it can wash away like earth so it's susceptible to water damage if not properly protected from water. As a garden retaining wall I wouldn't therefore recommend it because it's going to get wet frequently. They can use it on houses because the roof and it's overhang protects the walls from constant moisture.
If it's a particularly high wall you would normally put seep holes into the wall to allow for drainage. Naturally, even with plastic pipe in the hole I would think it'll not last 100 years. So if you're thinking of using rammed earth, I'd definably line the wall with plastic.
Also, earth does crack as it expands and contracts. You fix the cracks with more rammed earth mix. People with these types of houses generally have to patch cracks every few years for this reason. But, it's a very organic material to work with and they would be aware of this... it's a choice you make when you build with it.
You could use cement in place of lime. That may make it last a lot longer and increase it's strength. I've seen this work for some structures and it may require some experimentation being out in the open.
Concrete on the other hand does last a long time if properly prepared.
It also can crack as it naturally expands and contracts. To prevent serious cracking you need to cut it every few meters and fill the gaps with a flexible compound. You might notice that as you drive over some concrete highways you'll hear a bump, bump, bump, noise. That's the wheels going over the horizontal cuts in the concrete designed to allow for expansion and contraction and prevent cracking. If it's a big retaining wall you'll need these cuts.
Concrete is also porous so water can be absorbed. You can imagine that concrete that has absorbed water that freezes won't be good for the concrete right? Because it could cause it to crack, and it does. So you need to get a grade of concrete that is less porous and stronger (and make sure it's thick!). Talk to your concrete supplier if you got this route and make sure you get a stronger grade and that when the concrete is poured it is not too wet.
If I were you I'd consider using a different material all together.
Have you considered brick? You can get some flexible mortars so you won't get the same cracking issues as you would with concrete and it will look more attractive in my opinion.
Another option is to use a hardwood. Down here in NZ we call them railway sleepers. You can stack them, bolt them together and form a pretty nice retaining wall. It's strong and attractive. I'd paint the side where the dirt is touching it to protect the wood, or use a plastic barrier or paint on barrier like mulseal. It probably won't last 100 years but it should last at least 50 if well prepared and looked after.
By the way, some woods like Jarrah can last a very long time without any treatment. We can sometimes get Jarrah poles used by the electric company for the overhead wires. They pull them out of the ground and they are still as good as when they went in over 50 years ago. So, some hardwoods can really last.
Best Answer
Curved concrete drives and walkways are no more likely to crack than rectangular. I have a semi circular drive and a curved walk. The drive foundation was well packed and it has 1/2 rebar on roughly 18' centers ( we had some left over from the house) , it has handled 10,000+ lb. trucks, no problem . The walk, not so well packed and used only mesh : It has hairline cracks at some decorative brick inlays. So with good preparation and rebar you can make any shape you want.