Being practical, I would first try some pre-assembled ESP8266 boards at high temperature. Yes, that crystal will work but the chances are one very similar is already mounted on a pre-built module. You would save yourself an enormous amount of development time because the layout is very critical. You would essentially be building a duplicate of an inexpensive part at a much higher price.
Remember also that the ESP8266 alone is of no use unless you code for it in assembly language and keep the firmware very small. The reason most modules also contain a flash ROM is to allow enough storage for things like the ethernet routines, stack and buffers. On pre-built modules the firmware foundations are already present and you can simply call the routines as needed, all the hard work is done for you.
I would be cautious about using a steel shield over the device, they actually run quite hot if continuously transmitting and given your high background temperature I wouldn't advise you to restrict air flow around it.
Those component tolerances should be as tight as possible, they are the antenna matching section and anything that causes an impedance mismatch will reduce the range. As I have said before, I get ranges of more than 75m from bare modules with on-board PCB antennas without any problems. On the modules here, all those components and the crystal together occupy less board area than the IC itself.
Brian.