Please share with me your experience in building Data-Logger

I want to build a data-logger that records temperature and pressure every second for 20 hours. My circuit must work in a range of 20-130 'C and 0 - 9000 PSI ! And it must be inside a cylindrical chamber with a diameter of 25mm and a length of 45cm.
This circuit goes deep into the Earth to a depth of 500 meters, through an oil tube. so I must put batteries in the chamber.

• What are the points that I must consider? (Everything! Such as regulators for PIC, Type of batteries, Type of Memories? SD Flash?EEPROM? ... , Protecting the circuit of electromagnetic noises, ans so on)
• Which PIC is the best for this purpose? PIC16? PIC18? Which model?
• I must bought Extended Elements or I can use thermal insulation and use the same Industrial elements?
• Which PIC compiler is the best for Starting PIC with this project?
• What kind of sensors do you offer? Analog? Digital? and which one? (Name)
• Am I need a special PCB or it can be like other normal PCBs?
• Should I consider to design a reset circuit for Brown Out pin? If so, Why? and How?

I don't want you to answer all the questions. Please answer whatever you want (of above questions.) If the question is very terrible for this site, leave a comment,and I will remove it after 1 week :) I appreciate any any similar experience in building this kind of circuit.I am really a brand of new in PIC. So, please help me to build this circuit.