First, congrats and welcome to the sport.

Some suggestions per your questions (with the caveat that a discussion
with a CFIG that you trust is undoubtedly a much better source of
guidance!):

The cloud base question gets to the very heart of this issue, however
really only on a theoretical basis - cloud bases have been known to
vary quite a bit, cloud to cloud! And here it gets interesting,
because ceilings are given AGL for the field in question - because
instrument approaches have minimums based on how low the clouds are -
AGL! But cloud heights are given in MSL. Hopefully we aren't in the
situation of shooting an approach to mins in our gliders!

Tows are usually billed in altitude gained on tow - so it's really
difference between takeoff and release altitude. You got to do the
math - but since most pilots seem to like nice even tow numbers (odd,
since the good lift always seems to be at either 900 ft or something
like 1700 ft) it really isn't a demanding calculation to make. Anyway,
just release, and trust me the tow operation will figure out a way to
bill you! Seriously - at a strange field with an odd altitude, just do
the math before hooking up, and when you see that number, you are
there.\\

The "magic" 200 ft - if you still use it, instead of TLAR - is the same
thing, do the math before hooking up as part of your checklist (the E
of CBSIFTCBE, for example) and it will work anywhere.

For those who like a visual reminder, there are moveable "bugs" that
can be attached to the altimeter face that can be set at the field
elevation. Cheap and easy.

Kirk
66