If you’re not sure if it needs water, wait 3 days”

“The only way to kill a port is to water it too much”

One nice feature about ports is that they can go a very long time without water.  I’ve let trees sit for 3 months without water and they survived just fine. They were dry and stressed at the end of that 3 months, but after a heavy watering they plumped up and were happy as could be. 
How much water you give your port depends on many factors: Your location, temperature, humidity, what soil you use, how deep your pot is, etc.  Generally you want to let the soil completely dry out between waterings.  If your port sits in water for 5+ days straight it will start rotting.  I keep my ports in well draining soil with lots of drainage and I water once every 5 days typically.

As much as you can give it. Ports love sunlight.  As for minimum amount you should aim to give it at least 4 hours of direct sunlight or 8 hours of indirect sunlight.  Longer duration of sunlight and increased intensity leads to more compact growth and smaller leaves.  If you can’t give your port that much sunlight you should invest in a grow light to supplement.

This depends a lot on your watering schedule and location, but as long as your soil does not retain much water it should work fine. Miracle Grow Succulent Soil works well in most situations.  I like to use 50/50 mix of Pumice/Lava Rock because it drains well, doesn’t compact, and guarantees fine roots which is desirable for bonsai.

As a preventative I like to use Bonide Systemic Granules. You spread the granules on the soil and 3 weeks later the plant is protected.  The roots absorb the pesticides so that when a pest bites a leaf they die.

For treatment of an existing problem it depends on what pest you’re dealing with.  Likely you’re dealing with Mealy Bugs or Aphids, neither of which are difficult to treat.  Start by physically removing them by hand or with a q-tip dipped in alcohol.  If the problem persists you can use a product called “Seven” sold online or at Home Depot.  In shade: Spray the port heavily with Seven, wait 15 minutes, rinse off thoroughly with water, keep the tree out of direct sunlight until the next day.