1) What is the PSI of the (TE) flaps hydraulic system?
The trailing edge flaps are powered by hydraulic systems 1 (Inboards) and 4 (Outboards) which are pressurised to appropriately 3000 psi
2) Are the LE flaps still pneumatic?
Yep by bleed air. LE and TE flaps can also be driven by electric motors if their respective hydraulic/pneumatic system fails.
3) What is the air composition of the tyres?
I think its nitrogen gas only (not a mixture with other gasses but im not 100% sure) to a pressure of 200 PSI
4) Compared to the 777, does the 747 have greater redundancy in the flying controls following single and double hydraulic failure?
I've never flown the 777 but 747 has 4 systems of which any one alone is still capable of offering power to an aileron, elevator and rudder to give the pilot some control in all 3 axis.