Indeed welcome to the club! It's great to see other BRDM owners out there
Everything BRDMdriver has said is quite true, the hydrualic deficiencies with the clutch down or out of gear are quite annoying. Speaking to a freind of a freind who use to drive BRDMs back in the Polish army; mentioned that the reason this is done is to disable the front steering when the vehicle is swimming, otherwise under certain conditions could cause the vehicle to capsize.
However, there are ways around it, For example if trying to manouver in a tight spot - put the transfer case into neutral (moving the Hi/Lo range lever into the middle position), select first gear and release the clutch, you won't go any where but you will get power steering when stantionary.
For oils and what to use, check out the manual in russian truck forum, its got a section on wesstern alternative oils in the back. But we've found that the oils it recommends are really more for winter use and therefore you may want to use slightly thicker oils.
I've certainly found that in my BRDM as the transfer case overheats, it has the correct level of oil in it, but it's just too thin.
Anyway, look forward to hearing from you when she arrives!