Just like you, I've thought in excruciating detail what to do with my 40 gallon once I get it....
So here we go~
A: You could do 1 pair or 2 pair of angles (make sure you define them as pairs in the store). Then, the tank is 4 feet long... So it can house a Senegal Bichir! His mouth could fit over a neon or glowlight perhaps, but not an angel

And he'll get big enough that the angels won't be a problem to him.
You could then plant the tank, and perhaps add something else from your lft, like a shoal of 5 roseline sharks (

if you have 150 to spend on them... but if you planned on discus, this'd be a nice alternative). Just make sure you either get them while the senegal is small, or get them at 3" plus so that the senegal isn't gonne eat them. That'd be one expensive meal. Also, A false flying fox is a very nice fish to consider that most people toss aside.
B: The tetra tank.
for a four foot tank, that's a great support. Heavily plant it and leave a middle swimming space. Then you can have many different kind.
7x cardinal tetra
7x Black Neon Tetra
7x Glowlight Tetra
7x rummynose tetra
7x Lemon tetra
Now for the bottom dwellers.
7x Kuhli Loach
7x Some kind of small cories.
then you could add in... an army of amano shrimp, as well as some bamboo shrimp
20-40x Amano Shrimp
5x bamboo shrimp.
And that's probably the tank i'd go with if i were you, but only if you heavily planted it. Water Wisteria would be my choice in such a tank.... Byt yeah.....
You could also do one humongout Female Betta sorority.....
Like, 30x Female betta, Heavily plant it, and let shrimp run all over the bottom. like, 40x amano shrimp and 10x Bamboo shrimp. Dunno....
Just my suggustions
