Hi from Oz

I need some advice.  I bake bread weekly for myself.  Now I have an urge to attempt sourdough bread.  I know nothing about starters, but have been the recipient of 100g of mature white starter from a fellow poster (a baker by trade) on an Oz forum.  The donor amazingly lives just 15 mins from me, but as he was leaving for a month long holiday, he left me the starter in his letter box.  I collected about 1.5 hrs later.  His instructions were to feed 100g flour/65g water but  to just frig if not intending to bake for a while (maths not being my forte, I assume this is 65% hydration?)  Is this a good hydration for a white starter?  I think I need to feed and increase the base starter a little?  The trouble I have is this .. I brought it home and put it into frig am 28/12 (very warm summer here .. up to 40 dC some days). It was fed by the donor at 6pm on 27/12.  I transferred it to a sterilised glass container and popped it into the frig.

 When do I need to feed it next. .. in a week, or less?  It inhabits my frig and will do so between feeds.  I will not be baking until I have a little more starter built up.  There are just so many blogs, posts, books, etc. I am totally confused.

Unfortunately, I must have the bug .. I have given it a name already!

Sondra