In my experience one sachet of rehydrated, then chilled 34/70 is fine with a five gallon batch of small lager (1.044 or so), which I tend to make a lot. All yeasts seem to prefer starting below the fermentation temperature then allow them to rise into the zone. I brew 10 gallon batches and have great results with 2 sachets at low OG. The second gen, I use Mr Malty and find that it is recommending typically to pitch about 340 ml per 10 gallon batch - it is typically a little less than half of the collected slurry from a prior ten gallon batch.
When making a starter from liquid yeast, I tend to make a 1500 ml starter, run it out then chill and decant and add another 1500 ml of cooled starter wort and spin it up again. YMMV, of course!