Hi Ishan,
Answer to both your queries is:
1) Yes, you can install NW 7.3 ehp1 in a single stroke without any issues and this has been done by me for one of the client.
2) Media required for NW7.3 ehp1 is present in the link as mentioned by you above.
Apart from that you will be requiring
a) Software Provisioning Manager 1.0 (For installation of NW 7.31) - contains sapinst
b) Kernel 720 DVD
Regards,
Gaurav