Coming back to discus keeping after more than 20 years. Help me out.

Hello, that's right. I think I had discus 25 years ago and I want to come back to the hobby and a lot of things have changed. So, I need to do some planning. Hopefuly you can help me:

1. I want to use tap water, because where I live the ph from the tap is 6.8, and since I want a 600 liter tank, then doing water changes with RO would be a major hassle and expensive.
This is why I don't want to keep wild discus as well, but only discus raised in the USA that use tap. (I'm in Mexico, by the way)

2. For water changes: my idea was to fill up a big container with tap water, add Prime to the water, put a heater in it and heat it, aerate it for a few hours, and do a 20% water change weekly. I'm planning to use a very good biological filter.

3. For algae: I know that tap water means algae, there's no way around it. I have a 20 gallon planted tank and I only use RO to avoid algae. That's why, the discus tank will not be planted except for some anubias and microsorums and wood. I will also use sand. According to my experience, you don't see algae under low light conditions. Am I right about this? So, based on your experience, what kind of lights are you using to light up your tap water discus tanks? I've seen these Skylight Hyperspot which give discus an amazing coloration. However, I know they are strong lights (which can be dimmed though) I was wondering if I could use these lamps without getting algae problems? Anyone?

4. Heating: I live in a tropical beach town in Mexico. In my 20 gal planted tank I need a computar fan on 24/7 to lower water to 80 F. For 4-5 months per year. This is of course, no problem for a discus tank, but for the winter months (only 3 months per year) water in my tank gets as low as 70 F since I don't use a heater. Naturally, the discus tank would need to get a heater. I'm sure electricity bills wouldn't get that high, but do you see as something more cost efficient to put a lid on top of the tank to keep the temperature longer and spend less on electricity? Are there problems from having a lid? How much do you think you spend on aquarium heater? I know your rooms are probably heated anyways and this helps though. But what do you think?

Thank you.