No, you do NOT put separate shutoff valves inline to the tub valve. You should select a tub-valve which INCLUDES integral "stop" valves. Most manufacturers provide these at typically $15 or $20 more than the "plain" ones. I had a Moen 3170L put in which has quarter-turn with a screwdriver stops behind the cover-plate to allow servicing the mixing valve. Delta and Kohler both list such integral-stop tub-fill valves. Probably everybody else does too.