Hi Forty_44,
I would stretch gastroc and soleus, especially if they're feeling tight. That will also stretch tib post a little too. Static Stretching is usually best done after exercise/ running hold each stretch for around 30 seconds. Use a dynamic warm up per running with dynamic calf stretches.
Your calf raises should help strengthen tib post, although most of the work will be done by gastroc and soleus. When you do your calf raises, try and make sure the heel doesn't turn out, in fact you could try and work tib post a little harder by turning the heel and foot in a little as you lift, as long as it's comfortable.
Mixing calf strength work with stretches should ensure you gain strength without losing flexibility.