What are my options for SETV after multiple visits to Vientiane, and what are the agency statuses for each alternative?

Different consulates have a different number of tourist visas you can get from them before they'll warning stamp you. I think you can get 4 or 5 tourist visas in Vientiane before you get the warning stamp. BUT getting that stamp in Vientiane means you can't use Savannakhet either 　

There were reports that the consulate in Phnom Penh refused someone a tourist visa because they had a warning stamp from another consulate in their passport.

I'd say the best advice is bounce around from consulate to consulate rather than foolishly hitting the same one back-2-back..

What's the consensus now for how many possible in a row? I left for 3 months, came back and now on my "first one" again, will this mean I am good for another one or two?

Why did you keep hitting Vientiane over and over like that? If you go back you will probably get the warning stamp of too many tourist visas.

I agree with Amornrat, you're less than 4 hours away from the thai consulate in Savannakhet. Go there. Be prepared to show 20K baht in a bank account, and proof of onward travel.

Savannakhet would be the closest for you. Just head each to Mukdahan.