Interesting concept and execution, here are my ideas on how to expand and modify your project:
Tool Durability/Strength Modifications
I am not quite sure about the sword and axe having the same durability as stone, maybe both having the durability of wood (as with the rest of the tools) but with unique damage chart:
As you can see in this all cactus tools have the durability of wood/gold, but with every tool being slightly more powerful as an offensive weapon, with a cactus sword being slightly stronger then stone but weaker then iron, a cactus axe being as powerful a iron axe and pick and shovel as strong as stone.
Now this makes cactus slightly overpowered, but with using cactus tools there is an inherent danger;
There is a 1% chance when using a use of a cactus tool it will instantly break and do to the player the amount of damage the tool does (e.g. you are using a cactus sword to fend of legions of night, and said cactus sword breaks and kills you). Now 1% may not seem like much, but as every cactus tool has 33 uses, with that approximately 1 in 3 will fail on you.
Cactus spines can be collected by placing a single block of cactus anywhere on the crafting grid, in return you get 4 spines. A spine will be a basic ranged weapon, with half the range of a bow and with each spine doing 1/2 a heart of damage when they hit any mob (or you if you throw it up in the air). But the true use is not to simply throw it it the enemy but to throw it on the ground in front of them, with every spine the mob stands on, their movement is reduced by 5%, lasting 5 seconds and stacking up to 50%. Spines can also be used to make spine arrows, with do 1 heart of damage (compared to a regular arrows 2), but more on archery later.
Cactus armour would be made in crafting the same way all armour is made, but with cactus blocks. But cactus armour is unique in that it doesn't stop any damage to the player, but will take durability damage with every strike. Then what is the point of cactus armour? Simple, if you have all cactus armour equipped, whenever any mob touches you, said mob takes 1/2 a heart of damage, thought the damage is low it is rapid, as fast as being damaged by standing on a cactus. Cactus armour has the durability in uses as leather.
Growing Cactus Flowers/Fruits
Adding upon basic cactus growing, when a cactus becomes 3 blocks in height it starts to grow a cactus fruit, after half a day a cactus flower will have grown on the top of the cactus, another half a day and it grows as cactus fruit, which heals 2 hearts each (non stackable). The cactus flower can also be collected in the form of 2-4 cactus petals. If harvested the cactus will simply start the cycle again if it is still 3 blocks in height.
Border-Line Silly Ideas
Yes, cactus archery. A cactus bow is made in the same crafting positions as a normal bow, but with sticks replaced by cactus sticks and string replaced by cactus string, this is done by "cooking" a cactus piece in a furnace in which you get one piece of cactus string per cactus.
Once made, the cactus bow will be need a special type of arrow, because normal arrows don't work with it, so the cactus arrow will need to be made. This is done by using the cactus petals from growing cactuses as feathers, cactus sticks instead of normal stacks and cactus spines instead of flint. Each cactus bow will have the same uses as a normal bow (which is currently infinite), with each arrow doing 1 hearts of damage per strike, but with the same 5% slowing effect as the normal spines, with each debuff lasting 5 seconds, stackable to 50% (each attack renews the duration of the debuff).
Those are my ideas for the "Cactus Craft" project, make of the ideas what you will.
I have got a similiar idea to what the above poster thought. Poison
The juice inside cacti is poisanous,and you can cut out the juice to hold the poisan with a small tube.this does 1 damage every secend when in a arrow or sword.It stops on the 5 hit. A medium sized tube does 2 poisan damage and a big tube does 3 for.
= small tube 4
= medium size tube
= big sized tube
You can't do anything with a tube and cacti,so you must make a knife.
Now that we have done that,we can make the tube filled with poisan.
= tube(any) with poisan
  
  
= < small x 4>/ <medieum x2 or big x 1
Giving items poisan
Basicly,you just put the item and then put the poisan tube above it like so:
= Sword (any tier) and other tools including arows but not bows
= poisan tube again (any size)
= 1 arrow ( 1 so that it isn't overpowered)
Now you got a Poisan sword or anyother tool YAY!
im not good with grammar so don't mind it please XD
if tl;dr then basicly you can make poisan arrows or whatever.
Just noticed your new update, for some reason I think that the axe should have the strength of a stone axe, yeh know, for teh spikes, and also the hoe....for some reason I feel like that could be different.
Other than that, this is GORGEOUS.
Well, what is the point of the Cacti tools without trees if they require sunlight to grow? I think you should make a kind of addition to this mod: crafting cacti with something will make a cacti GrowPoint that allows you to grow them even in full darkness. That makes cacti tools giving more sense...
I guess people will say;
"What's the point of a chisel??///11!"
Well, when you're hollowing out a room in a cave, and you see some iron, or coal, you dont want your room to look ugly, do you? so you use the chisel to keep the room looking nice, and you get the ore!
You pointed out that the specific ore will have a chance to drop 2 times. Yet, judging from your post, theres currently only a mod-specific version of either the gold and the iron ore.
so what about the rest? Would´nt it be possible to oh shizz i forgot gold and iron are the only ores dropping ore blocks.
Never mind :biggrin.gif:
Ill download the shizzel now.
Not found any diamonds in mah new world yet, so u got a life-lasting supply of from me instead :biggrin.gif:
There is only one thing missing in this mod that would make life in a cactus dessert possible without trees and that is doors I know they are not neccasary but it would make a house of cactus easier to go in and out of