Totally fine to add T5 bulbs. Just reduce your intensity on the radions accordingly or simply start the T5s at very low duration periods and add an hour per week. Ideally, you'd want to be measuring par or lux so you have a better idea of how much light you are adding in with the addition of the T5's.
As far as bulb choice, it's going to depend on what you're trying to accomplish. Actinics are going to give you a deeper blue hue to the tank and create more "pop". I'm not sure you'd need two actinic bulbs, though. Blue plus is a pretty good overall bulb you could pare with the actinic. If you find the color is too blue, you can easily increase your radions white channel, green, and / or red channels to compensate to get the overall tank color you like visually. If you want a whiter tank, a coral plus bulb is a good choice.
