I want to give him more room to swim, so is it okay to disassemble the barrier? Is there a chance that Blueberry could catch dropsy?
in theory no, since dropsy is an internal disease but if you are worried about the infection spreading in some way then do a chlorine bath (only do this if your barrier doesn't allow water through) you just add a tablespoon of chlorine and let It sit for 30 minutes after that do a 100% water change and use 3 times the amount of conditioner you would normally use.
-What safe (cheap) driftwoods are there?
I really like manzanita and spider wood, they are quite cheap where I live.
-Is sand substrate good for live plants?
yes and no, it allows the plants to set roots quite nicely but it doesn't give them any nutrients, for this, you have 3 options:
1. only use stem plants and epiphytes: (stem plants get their nutrients from the water column and the substrate as such they won't suffer a lack of nutrients even if planted in plain sand, and epiphytes don't go planted in the substrate they go attached to wood and stone (if you do plant them they will rot) as such they also take their nutrients from the water column
2. you can use root tabs: just put one at the base of a plant and it will give it nutrients for a whole year (use slow-release ones)
3. (and my favourite) do a dirted tank: you first put some topsoil or potting mixture on your tank and then on top of that you put your decorative sand, this will give your plants nutrients for up to 10 years and will also give them carbon to build their new leaves, the only problem is that you need a substrate aerator (like Malaysian trumpet snails) because otherwise you are gonna get methane bubbles that will not damage your plants or aquarium but will make your substrate look bulged and loose, which can be a bad look sometimes, this is because as the soil decomposes in a low oxygen underwater acidic environment it releases this gases but they can't escape without help (it sometimes can escape so don't get scared if you see bubbles coming from your dirted tank) this is actually what happens in peat swamps so if your tank lasted like this a few hundred years you would get peat, and as it is covered by another substrate (sand) if given thousands or millions of years it would become coal, or petroleum.
-I don't have a tank light, are there any plants that could actually grow? (if I need one, where can I get one?
there are some lowlight plants for sure but an aquarium light is still recommended, look in Amazon, eBay, or your LFS for some plant growing aquarium lights.
-If I took out the silk plants in the tank, would it mess up my cycle and get rid of beneficial bacteria?
yes, it would take out some beneficial bacteria, but it wouldn't get rid of all of them since most live on your substrate.
and filter media, as such no, it wouldn't mess up your cycle
hope this helps