Yes, Altums are the largest angels. Just don't get true Altums unless you are very experienced; otherwise, you will waste a bunch of money on dead fish. Most "Altums" on the market aren't true, so that shouldn't be a problem. Personally, though, I would pass on the angels; I had an angel with a BGK, and it was constantly nipping at its fins (usually, it was at night, and occasionally, I saw this behavior during the day).
Instead, I would do either Electric Blue Acaras, Silver Dollars, or a larger Cory Catfish species (Brochis Corys are very fun. Or Sterbai; I never kept them, but they are beautiful nonetheless. If you like the look of the green color of brochis corys but not the size, go with Emerald Green Corys. I've had those, and they were great.), or Striped Raphael Catfish. I always reccomend Striped Raphs because they are just the hardiest catfish ever. Like seriously, ever lol. I have two of them in my tank now, and they cause no problems. One of my raphs has been with me from the beginning and has seen many tank mates, including a BGK (which, btw, they were best friends, always hanging out in the same spot together despite there being multiple hiding areas).
As for the others, Clown Loaches would be fine, and so would Ropefish. Personally, here are the setups I would consider for your tank:
Setup 1: 1 BGK, 10 Sterbai corys (or 10 Brochis or Emerald corys), and 5-6 Silver Dollars (I re-read your original post and you said you had a planted tank, so this might not work if you intend on keeping the tank planted).
Setup 2: 1 BGK, 6 Clown Loaches (make sure to take into account the full size of these loaches, not just their current store size), 4 EBAs
Setup 3: 1 BGK, 3 Ropefish, 5-6 Silver Dollars or 4-6 EBAs.
Setup 4: 1 BGK, 1 Bala Shark, 1 Striped Raph, and 4-6 Clown Loaches. (Make sure to do research on this one).
I hope this helps! Sorry this is kinda lengthy Lol.
