I wouldn't add the light just yet. Track the numbers and see what you are getting on average. If you end up needing to raise the temp the heat lamp pointed at the front will work just fine. I have heated plenty of tubs with lamps over the years when in a pinch. I would use the 100w with a dimmer. Start out low and gradually raise it until you have it just where you need it.

The heat tape will raise the temps but it is not designed for that and is not the most effective method of raising ambient temps.