Brackon

I like harder to find fish but my perfect 7.5 gallon would be 6-10 Aspidoras pauciradiatus and then 8-16 Barboides gracilis. If you are really wanting species tanks then I would say getting a group of rosy loaches would be fun as they are super active. If you were to go ultra jungle and let plants get super dense I would say you could try some elassoma as they are very similar to Scarlet badis or red tiger dario as they are becoming more and more common and the few times I've seen them they always have a better male to female ratio than Scarlet badis.

This is how I move my tanks or size up my tanks and it typically works but personally I always keep an eye on it and do a few small water changes over the first 2 weeks

Yes the humidity will still be more than a typical room but with about 300-500 gallons of water you should be okay with a dehumidifier although venting with a bathroom fan would also work. On the topic of keeping the room warm it depends on how cold it is where you are pulling new air from. If its from the other side of your shop it should be fine as long as it isn't anything below 40 F as the air turn over will probably be small enough that your heater will barely notice a difference. My personal thoughts at least. Personally I would use a humidifier and figure out how to hook up the water reservoir so that it drains either straight outside or down a floor drain if you have one.

I would say unless it goes completely to mush just leave it and it may surprise you. I recently found 3 stems of S. repens in my basement that is still alive, long and white from being light starved but still alive in barely any water.

I think it has some nutrients depending on brand but not much. It does however serve as the perfect medium in which the roots of aquatic plant can grow. This is my personal opinion but I've had much better luck with it than gravel or sand and it just looks good to me. I always use liquid ferts anyways but I'm sure for heavy root feeders tabs would be appreciated.

Is the rhizome rotting? thats the part the roots and leaves come out of for context. I know some anubias don't like being superglued. Also they can go through a melting phase before growing again once they are moved much like crypts

Getting more is definitely better. There is something much more natural in their movements when there are more than say 15. I had 25 silver tip tetra in a 33 gallon and it was one of my most fun tanks

I second all of these and add crypt usteriana and any sword plant as my 2¢

I haven't bough fish online in 3 years but I know theres the community run aquabid and getgills. You could always try contacting the wetspot too they are only 2 hours from me down South in Portland Oregon so I just drive down there but I know they ship but they have a minimum order size and minimum order price so unless you are getting lots I'd say just talk to your lfs. Most local fish stores will work with you on special orders. Theres a lot of things on their fish lists they won't get just because they don't sell but if they know you will for sure get say all 20 they order then they typically don't mind.

My grow out bins as they are not actually tanks are all emersed. This means no algae and no need to run CO2 since they are in the air. I did this as I used to grow anubias this way years ago. When I broke down my high tech planted tank a few years ago this meant I didn't have to throw away my plants or watch them melt and now that I'm creeping back into planted tanks I don't have to buy everything again just pluck from my bin.

Personally I like nano stuff and that could work for you but that means they are more skittish normally or are easily out competed for food. I would go for something small but not a true nano fish, something like a neon, cardinal, green neon or any tetra that stays under 3 inches but be wary even some small tetras might predate guppy fry. Asia also has lots of fish to offer with most danios and rasboras being good candidates and some smaller barbs might catch your eye. Personally I like Microdevario kubotai/green neon rasbora, Sundadanio sp/blue neon rasbora and Brachydanio tinwini/gold ring danio. These have been in my tanks for the last few years and all school to some degree and are small enough that guppy fry with any amount of cover should be able to survive.

I like Pogostemon stellatus 'octopus' as you can trim it short or let it grow tall and it can sweep around and cover the top of the tank much like vallisneria but easier to grow in my opinion. Most rotala species are also pretty easy and will grow under any light. Hygrophila difformis/water wisteria and ceratopteris thalictroides/water sprite are lacey fast growers too which can quickly fill a tank. On the slower growing side you have anubias which along with java fern are basically bulletproof and I see you already have some of each. Crypts are also slower growing and the most common wendtii (green, brown, red, tropica) are a personal favorite. Then there's larger ones like blassi, pontederiifolia and usteriana along with smaller ones like parva, lucens and lutea.

Did you ask any questions about those particular fish at the store? I typically frequent my local stores enough to know what is new but a few questions might be; are they eating, how long have they been in the store, any medication, were there more and they died or were bought and if so have those people reported their fish are fine. Stuff like that is useful just so you know what type of fish you are getting into. It sounds like everything was fine though and you just got unlucky and got a stressed out fish

IMO a guppy tank is good by itself and adding a schooling fish could make it look a little chaotic. If I was to do it anyways since you say you want to I would go with a color that is opposite your guppies so they compliment each other. Pearl Danios would be perfect for a 40 but they are pretty energetic so just keep that in mind because they won't let any flake food hit the ground.