Can home-made mozzarella be made in small batches (quart of milk instead of gallon)?
I've done this and it'll work, but your yield will be small.  With a gallon of quality milk, my yield is about one pound of mozz. Divide that by four and it ends up being about 4 oz.

Use an appropriate size pot and microwave container... And use a thermometer.

I've only used liquid rennet and I don't think there's much difference in dissolving the tabs.

I've also found the process to be somewhat forgiving on close but not exact measurements of ingredients when using good quality (non UHT - NOT ultra high temp pasteurized) whole milk. Other milk not so forgiving and UHT milk just ended up as ricotta.

The microwave process heats the curds to extract as much water out of them as possible, then they become soft and stretchy and can be pulled and kneaded like dough. Heat, extract, pull, knead, repeat.

Don't be discouraged if the first batch isn't quite perfect. It'll take longer than 30 min. your first time - you're going to keep wondering if your doing the whole microwave process right or if it's hot enough. 

A great site for questions and instructions is http://www.cheesemaking.com.  

Their FAQ addresses reducing the quantities in half (#5) and how to dissolve and reduce the rennet tab - http://www.cheesemaking.com/store/pg/242-FAQ-Mozzarella.html. 

Their 30 min mozz instructions with pictures to see how everything looks along the way http://cheesemakinghelp.blogspot.com/2010/12/making-mozzarella-with-anya-age-10.html