Hi Magpie, answers below each of your questions.
1) My tank pic is attached. I recently ripped out a bunch of plants for more swimming room. Does this look OK? Would you change anything?
My main concerns are actually regarding the two wood pieces. I've seen discus swim and they are actually a lot more agile than I anticipated, but I would happily take out one or both, or move one or both of the wood pieces to better suit them, or just get a new piece of wood. I so love the aesthetics of wood in a tank, but will remove if necessary.
Nice tank but I would suggest moving any plants to the rear of the tank to allow swimming room for discus. I would leave the wood.
2) Size/age of fish. I know that I cannot grow out the small guys in a way that is healthy for them in a planted tank. But large fish are of course more $. What size would you recommend starting with? Hans said anything 4" or larger, but I wonder if I should do 4.5 or more?
Six sounds good.
3) Current inhabitants. (12 rummynoses, on the younger side; 5 huge old cardinals; 8 big old white-tipped tetras; a handful of nannostomus eqqus; 1 BN plec, 1 para plec (worried about her and the temp); 6 kuhlis.)
Should I move / rehome some? Hans said no. Wondering about the bioload, however. I have an Eheim 2217 canister.
Research the fish you have in there now to ensure they can handle the higher temps. I know the tetras should be fine.
4) Number of discus. Hans said 6-7. My LFS (The Wet Spot in Portland, OR, reputable shop) said 5-6. Maybe 6 then? I was thinking of starting with 4 and adding 2 more later so I don't have to spend so much money. I think that 3 to start might be too small a group... so it will be spendy either way, but less so than adding 6 larger fish at once.
Best to buy the whole group at the same time. Less time in QT and the group dynamics will not change when adding more fish later.
5) Heater recs. I have an Eheim Jager 150 w and it has been going strong for 5 years. But... am worried that it is getting older and won't be able to handle the higher temp required. I'd love brand and size suggestions.
I will leave the heater recs to others
6) Temp. I have gradually increased it over the past week or so, and today it is at 82.5 I know this is at the lower end of the temp range, but with the plants and other fish, I think this might be a nice compromise. Yes or no?
82 is good.
Some other considerations is thoroughly research discus now before you get them. Decide on how and how often you wish to do your water changes as doing water changes is critical to maintaining healthy discus.
Pat