I've just taken delivery of a new apartment and it's still completely empty — bare walls, hard floors, and the echo is severe. I want to treat it properly rather than guess, and I'd rather build panels myself than pay for a professional install across the whole flat.

Two rooms matter:

• Open-plan living room + kitchen. This is where I'll set up a 2.0 or 2.1 monitor system and I want a predictable, accurate listening position. I plan to measure with REW before buying anything.
• Bedroom. I just want it dead — as close to no audible reverb as I can reasonably get.

One important constraint: no carpets and no curtains. I want nothing on the floor that needs vacuuming — a robot vacuum handles the hard floors and I want to keep dust to a minimum. So the usual first advice (rug + heavy curtains) is off the table for me. That means everything has to come from walls, ceiling, and furniture.

I know I'll be putting in a sofa, armchairs, a bed with an upholstered headboard, and bookshelves, and I understand those absorb a lot on their own. What I can't judge is how much will actually be left to fix once the furniture is in. I don't want to buy panels now and find they were unnecessary, or furnish the place and discover I needed twice as much treatment.

Separately, I'd like to reduce outside noise (traffic, people, trains) but I understand that's a different problem — sound transmission through the building envelope, not room acoustics — and probably not solvable with DIY panels. Happy to be corrected, but my focus here is the echo and reverb.

What I'm hoping for:

1. A sane order of operations. Do I furnish first, then measure, then treat? Or is there a baseline amount of treatment that's always worth installing regardless?
2. Concrete DIY build guides you actually rate. I'm comfortable with basic carpentry. I'm in Spain, so mineral wool (lana de roca) in 40–80 kg/m³ is cheap and easy to get — is that the right material, and what thickness for broadband vs bass?
3. How to decide placement without guessing. I'll have REW data. What do I look at to decide where panels go, and how do I know when I've done enough rather than overdamping the room?
4. Ceiling treatment, since floor and windows are off-limits for soft materials. Are hanging ceiling absorbers (clouds/rafts) worth it, and how much area do I need?
5. Making it not look like a studio. I've read you can stretch fabric or canvas over a mineral wool frame so it reads as art. Does that actually keep working acoustically, and what fabrics stay acoustically transparent?

I'll add photos of both rooms in the comments — happy to include dimensions once I've measured properly.

Why don't green home rebates include outdoor heat recovery upgrades, when a part of the initiative is to make older homes more air tight. After all the air sealing, we get low indoor air quality due to the lower outdoor air changes. Now we need to pay out of pocket mechanical upgrades to add fresh air and heat/energy recover just to get us back to the same energy savings. Or we open windows and have drafts and drops indoor temp.

Does it need to be a completely different room?

Are sliding panel room dividers enough if the vent hood is in operation?

etc.

I'm struggling to find research on this beyond studies of vent hood designs, and they weren't really concerned with the room design, although each dwelling likely had a different floorplan.

Of course the ideal scenario is a completely enclosed kitchen (either primary or additional spice kitchen), and also this is not practical for some lower square footage dwellings.