The Meguiar's Tan pad are very soft and have less mechanical action then the current black foam they use on the So1o pads and SoftBuff 2.0 pads.
As far as the Lake Country pads the RED and BLUE pads are IDENTICAL. Proper Auto Care orginally brought the RED pads to market and had an exclusive on them, as an alternative to the more common BLUE foam sold by other retailers. It was to be different. Same foam, same action, different color.
After the exclusive contract ran out, some other stores brought in the RED pads and choose to market them as different, which is not true.
While none of the foams are completely equal I would match them as such...
Meguiar's Black Foam to Lake Country Black Foam- These are very close foams and both have a very light polishing action on most paints.
Meguiar's Tan to Lake Country BLUE/RED- The Tan pad is very soft and has very little mechanical action which would be very similar to how the BLUE/RED pads work.
Depending on how you choose to use 3M Ultrafina (Ultra Fine) there should be no problem using it with your current inventory of Meg's pads.