Electronic – Rule of thumb for surface tension when placing components on the secondary side of a board

In general, I would say keep the top-side pour; it certainly does no harm, and it has some secondary benefits, such as less etching required and less thermal stress on the board during reflow.

You do still need to pay attention to current loops and place the vias appropriately, not just scattering them about randomly. Since the FT232R is the only active chip on the board, focus on its outputs. There are two LEDs that are powered by V_USB, and a few outputs associated with the serial port that are powered by V_CC. Where do the currents flow when any of these outputs change state? Try to keep the paths as short and direct as possible.

Note in particular, the ground path for the USB connector in your non-pour example. It has to go down, cross below the chip, then come up on the right before it gets to the ground pins on the top of the chip. The top-side pour shortens this considerably. In either case, it would help if you adjusted the vias near pin 1 of the chip so that the bottom pour is continuous there.

One side point about your design: Try to avoid having three etches come together at an acute angle, like you have on your Vcc trace. Make that a right-angle tee connection.

Yes, this can be done. However, boards with components on both sides will cost more to build up because it requires extra steps. As you say, you don't want the chips on the bottom to fall off while the ones on top are being soldered.

This is usually dealt with one of two ways. When the part has low weight to solder pad area, then it will stay in place just from the surface tension of the molten solder. For heavier parts, usually a kind of glue is used.

Double-sided boards are common enough, but when doing something like this it is still a good idea to talk to your assembly house first to get some idea what their processes are and what you can do on your end to make things simpler for them, and therefore cheaper for you.