Been reading the site a bit trying to learn my options

Looking at buying a (small) house, with one somewhat small bathroom, but a larger laundry/etc room. It's on a slab foundation. Has a septic system. Can't beat the price and location, but would really be necessary to have at least a half bath for elderly/disabled guests.

There's a utility sink, and the washer drains into that, which drains into the wall. There's also a hot water heater on the same wall in the opposite corner. There's an external door next to the HWH that somewhat complicates placement, but we could work around that. We'd like to add at least a toilet if not a stall shower.

We're contemplating switching from baseboard heat to heated flooring, so that might give an ability to hide some pipes or connections.

Without having the ability to poke into walls or concrete, is there anything I can easily look for to see if we'd have the ability to tear up minimal concrete and connect to a drain?

Understanding that we might have to raise up the shower a bit, is there anything that would stop me from going with one of the saniflo-type systems?

I'll try and draw up an approximate layout in the morning, but need to get some sleep.

Thanks

"Without having the ability to poke into walls or concrete, is there anything I can easily look for to see if we'd have the ability to tear up minimal concrete and connect to a drain?"
Yes, you could place the connection for the new bathroom group outside in the sewer line along with the vent running up the outside wall just keep the toilet and the lavatory on a outside wall.
Most bathroom groups are roughed in like this.
Toilet connects to sewer main. The toilet wet vents through the lavatory vent. Lavatory connects to toilet drain and runs a vent out the roof or revents back into a dry vent in the attic off the top the stubout tee. The shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes but also The Standard Plumbing Code Book.

"Understanding that we might have to raise up the shower a bit, is there anything that would stop me from going with one of the saniflo-type systems?"
A ejector system isn't needed in slab homes. Regards, Tom

So we'd have to dig in to rough in the toilet/shower.

Do I need to cut concrete all the way through to the outside thus interfering with the wall, or can I somewhat tunnel under it?

Once out, I'd make a dirt trench around the house with correct slight down slope for gravity until I hit the sewer/septic line and tie in out there?

Is the main drain generally low enough that I'll likely be able to make it around the house without getting stuck with gravity requiring me to be under the pipe?

I'm assuming that proper gravity will allow the sewage to leave the line and I won't have any freezing problems like you might with supply lines that are stagnant?

Do I need to cut concrete all the way through to the outside thus interfering with the wall, or can I somewhat tunnel under it?
Is the main drain generally low enough that I'll likely be able to make it around the house without getting stuck with gravity requiring me to be under the pipe?
It depends on the depth of your sewer as to the fall. You can roll the slope back to 1/8th inch per foot if elevation's tight.

I'm assuming that proper gravity will allow the sewage to leave the line and I won't have any freezing problems like you might with supply lines that are
Stagnant?

If there were no freeze problems in the past then I can't see any down the line. Good luck, Tom