Whatever you do, man, do NOT let on that you are suspicious. That could push this thing far underground. You've already got a lead with the VAR, so good job following what others suggested on your original thread.
I know this is tough. One of the toughest things you're gonna go through in your life. BUT...right now you are in control because you have a head's up. I didn't have that kind of luck. I had to discover my wife's affair on my own by finding a hotel receipt that she forgot to delete from her computer.
If you can find someone to watch you kids next Saturday, do so. If you have any family member around or close friend you can confide in you need to utilize them as a resource and do as a few have said here: Follow her.
The idea of meeting him on a Saturday is, IMO, pretty bad. My wife did the same thing for one reason...she knew I would be home with our children and wouldn't be able to leave the house. It was all about controlling the affair and it's exactly what your wife is doing here.
My advice is pretty much the same as others. Have a trusted person watch your kids next week without your wife knowing it is set up. She can NOT know. Your sitter literally needs to be in the shadows waiting to come into your home as soon as she leaves so that you can immediately get into your car and follow at least a block behind. Think Bond kind of stuff here and use your head. I would bring a good digital camera and make sure the flash is turned off. Not to catch them in the act or anything, but simply to take a picture of her car outside his house.
Then leave. Do NOT confront two people at the same time. You never know if this POS might have a firearm in his house and if you come to his door, he could easily see that as a threat to his property.
She's already been with this guy. Unless you don't want to go as far as I suggested, then you need to confront her this week. Try to get more VAR evidence, but again...do NOT reveal your source when you confront. Forget her phone. She ain't letting it out of her sight and all you need to do is look at your on-line billing to see what numbers she calling/texting.
Sorry for rambling here. It's early and I haven't had enough caffeine yet.