What spacing is needed between aircraft parking stands?
The Aerodrome Standards manual, which is based on ICAO Annex 14, gives the following values:

Clearance distances on aircraft stands
3.12.6 An aircraft stand shall provide the following minimum clearances between an aircraft using the stand and any adjacent building, aircraft on another stand and other objects:
Code Letter | Clearance
A | 3 m
B | 3 m
C | 4.5 m
D | 7.5 m
E | 7.5 m
F | 7.5 m

A references for the ICAO code letter categories is available here: http://www.skybrary.aero/index.php/ICAO_Aerodrome_Reference_Code