It must be dirt cheap
If you're not using a crystal just to keep costs down, why not get rid of the MAX IC, DB-9 connector, supporting caps, and just design-in a 5-pin header for in-circuit programming?

The PGD and PGC pins could be used for serial communications if you need to monitor what's happening on the board.

If this board will be installed outdoors, you're most likely going to have issues when attempting to boot-load new firmware anyhow due to changes in temperature. The internal osc is fine when indoors, but when exposed to extreme temp changes it will drift considerably, and you will have major problems just trying to load new firmware.

You won't have that problem with in-circuit programming. A Pickit2 could be used for firmware updates & as the serial monitor if needed, and a Pickit2 costs even less than MCS+.

Your board is a lot less expensive, and your programming tool is less expensive + more reliable, and you can use any internal osc speed you prefer.