The oil filter housing - I'm having a hard time finding a socket large enough to fit it.

I have found a strap which might - might - loosen the thing, but the cap clearly states 25nm.

Question is - is such tightness actually necessary? Can it be hand tightened like other cars or am I actually going to need to find the right socket and tighten it with a torque wrench?

Right bugger this is!

25n/m is only 18 ft/pounds (i.e with a 6 inch spanner pull 36lbs ish) . The rubber ring seals it so a little less probably can't hurt. For my first services I used a plumber's adjustable spanner - the contact area's big and the force is small. Now I use a tube spanner and a six inch bar. Much cheaper than a socket. Easy. It's also quite useful to leave the cap off until everything else is done so that you can pour the new oil in through the filter housing; much easier and less back-ache than reaching over the engine.

Apologies for the dog's breakfast of units.