Hi Frank - yes after building things in this way as individual separate surfaces that are next to each other you then usually want to join the surfaces together so that they have a shared joined edge between them rather than being totally separate objects.

Although you can use Boolean union to do that, I'd generally recommend to use the Edit > Join command instead for this type of combining (when combining along shared edges). That's because the booleans are more focused on trying to intersect objects and potentially remove material from them, so they will go through some extra calculations to try and determine if the objects being unioned need to be cut up. The Edit > Join command on the other hand is only focused on gluing edges together and does not attempt to do any intersection or cutting step at all.

And yes for doing the regular edge-based filleting that's done on joined edges so you want to get the pieces joined together after you have built surfaces.

When possible it can be nice to keep things as solids more throughout the entire process and carve pieces away using boolean operations rather than building individual surfaces. That can then avoid needing to join things together as a separate step since they stay joined throughout. But it can also be helpful to work at the individual surface level for building more complex models as well, that's why MoI supports either way.

When you work at a surface level you will end up doing some more manual joining steps.

- Michael