Those are all burundi as everyone has stated, they are not mpimbwe. I wouldn't pay that for any of those fish, but I don't know how it is to get fish in your area. I can get all of those fish for way cheaper where I live (minus the plecos, I don't know about them). Its up to you what you want to pay, if you think its worth it and if you like the fish. I wouldn't buy from someone who is selling there fish and can't ID them.
As for how many in a 140g, I would agree with 6-7 max, I wouldn't add more then that. I have a 150g and I had 12, now I have 10 (sold a few) and I am about to sell a few more. Its just to many for that size aquarium, even with over filtering. I will probably end up with 6-8 by the time I weed out and sell some of the fish. I wouldn't add in all the other fish that person is selling with them either. The syno cat is fine if you don't care about breeding (I have one). The other fish are relatively small and I wouldn't put it past the fronts to eat them if they catch them. I've had several rock dwellers with mine and it never ended well. If you have a large enough aquarium and a lot of rock-work then it works out better, there are great larger set-ups that I have seen on here with a cool mix, but most of these set-ups were 180g+ (that layout makes a huge difference). Not mention that is a lot of fish for your size tank, you would need some heavy filtration. Fronts are decently large and they are going to have a decent bio-load to go with it. (this is ime anyway).