picked up a 1991 suburban need some advice on lowering it and audio

[NCD1966]

I picked up this suburban the end of January for a really good price. My plan is to daily drive this to keep the miles and dirt off my 2018 GMC, The Burban is in really good shape mechanically other than some minor fixing. Engine bay is like it was new. I had some brake issues so I replaced the front hoses and calipers. The hoses were stock! now I have a axle seal leaking. You can see in the pic its leaking on my driveway.

Needs some paint and the interior is in great shape; pretty clean and no tears or stains. front seats have some wear but the rear seats look almost new. All wiring is unmolested everything works. Sorry no interior photos at this time.

I want to lower it with a 4/6 drop and add in some speakers. I like my audio sounding clear. So Im looking on speaker brands and locations in the truck. Really dont want to cut it into the truck much but Id like to have nice audio like I have in my 2018 GMC Sierra.

As far as lowering it; looking at the rear if I do a flip kit, I dont think will fit. the leaf springs look very close to the frame as is. I dont know if they were overloaded. I'll post up pics later of that. My plan is to do a 4/6 drop and add 20 inch junkyard dog type wheels.
tell me your thoughts.