Hi and welcome to the forum and the sport!
Yes, you will want a speed sensor because:
1) It's a pain to have to calculate your speed.
2) You might forget what gear you were using for an effort. When you train a lot, you it's common to change gears a couple of times per session.
I would look to get separate speed and cadence sensors. Put the speed sensor on the fork and the cadence sensor on the chainrstay by the crank. Why? Because if you have a combined speed/cadence sensor mounted on the chainstay, it assumes that your rear wheel magnet won't move because you have a road bike and your wheel's position is fixed. On a track bike, your rear wheel's position changes with each gear change...up to nearly 2 inches. This could affect if the sensor picks up the magnet or not. Yes, you can remember to move the magnet, but you will forget sometimes.
If the speed sensor is on the front wheel, then it's in the same position every time.
Mount the magnet on the brake track of the front wheel using outdoor double-sided tape. Why? Because if you mount it on the spokes of your training wheel, you may not have the same position available on your race wheel. The brake track is the same location on all wheels and you never use your brake track on track bikes. So, if you put magnets on the brake tracks (both sides) of all of your front wheels, you never have to think about anything. Just put the wheel on and boom...speed sensor activated.
Bontrager used to make separate ANT+ speed/cadence sensors. Not sure if they still do.