You lose about 1 degree of cam timing for every .010" milled. I doubt that on a stock motor with a stock cam, 1 degree would even be noticeable, but if anything would move the power band a hair higher.
Speaking of head gaskets though, there are so many different ones available, and they vary in compressed thickness from somewhere around .030" to probably better than .060" or so. I'd love to find out what Toyota originally spec'd the compression at, so there would be something to go on, and then start measuring old gaskets.
Quite frankly, I wouldn't sweat anything less than .010" at all. Also remember, the cam timing you may lose, may be more than made up for in compression increase.
And no, the tensioner cannot make up for it. The tensioner will take the slack out, but can not make up for the milling in relation to cam timing.