Many of the sauces I wish to make require broth or stock. I quite fear the preparation which requires lengthy cooking and dedicating more precious storage space for the finished ingredient. Is using store bought broth or stock a good alternative? How close does it come to the real thing? 
All excellent information, but can I answer bluntly: none of them come even CLOSE to the real thing. Once you use fresh stock, you will never, ever go back. Really. Making stock is easy, cheap, and as said above, unattended time. Stock forms the base of the kitchen, once you have it, you will notice the taste of everything you make improve so much. Get some bones (most butchers will give the away for free, just become friends) cold water, bring to boil, throw away the dirty water, start again with fresh water. This saves you the trouble to skim the grey foam, which is the white blood cells and other bitter tasting substances. It is also much more effective as skimming. And it results in a clearer, better tasting stock. When you do it, you will see what I mean straight away. I even rinse the pan  Add onions and celery, and basically all the cut-offs of all your vegetables. pepper corns, bay leaves, unpeeled garlic cloves, whatever you like. You dont need to peel the onion. The fuller the pan, the better the stock.  On your storage problem: two solutions. Big restaurants do not store, they just have a big pan boiling night and day. Small scale: after a hours or a night of slow boiling or so, remove bones and veggies. Cool. When fat is solid, remove and use this for frying: fried taters, etc.  Now boil down the broth, really down to say 20 percent.  You have a demi glace now. Put it in ice cube trays, and freeze. When frozen, remove, and put in bags. You have now concentrated fresh stock that takes up no space, and you can use in any quantity you require.  Please try it. Again: NOTHING comes close to the real deal. 