Best way to set serial port speeds on boot?

Install the setserial package. It can save serial port settings and restore them at boot time.

Alternatively, run a program when the port is detected via an udev rule. Put something like this (untested) in /etc/udev/rules.d/zzz_serial.rules:

KERNEL=="ttyS1", RUN+="/bin/stty -F /dev/ttyS1 19200 raw -echo"

Not to my knowledge.

The /etc/rc.local file is the best location for creating customization that are specific to the box. It was specifically created for these types of custom changes and is the first place that most system administrators are conditioned to look when dealing with Unix/Linux boxes.