Double-sided Assembly

You can find some good and relatively modern information in this document.

WEIGHT LIMITS FOR DOUBLE SIDED REFLOW OF QFNS Sasha Smith, David Connell and Bev Christian

Although their tests were for QFN packages, they work with the ratio of total pad wetted area to package mass. It will vary a bit with the solder type as well, in the paper SAC305 (96.5% tin, 3% silver, and 0.5% copper) is used.

They also refer to an older "rule of thumb" formula in unpleasant mixed units:

\$\frac{\text{Weight of the component (grams)}}{\text{Sum of the area of all solder joints (square inches)}} \lt 30\$

Of course you can always glue the parts. It's often possible (and often desirable) to keep all the heavy parts on the "top" and lighter parts on the bottom.

There is no equation for max part size. It will depend on your pad geometry and stencil geometry and the resulting surface tension. In production, unless it's a standard jellybean component that the manufacturer knows won't fall off, I see glue pads. Designing a board with massive components on both sides is bad DFM practice.

Also, you can certainly hand solder those parts you show below. I've soldered similarly difficult parts on multilayer boards using a SMT hot plate (example) and a hot air gun from the top.