1.) A good starting exercise is to build a basic missile cruiser. It needs to have decent speed, engineering sufficient for 2-3 years of maintenance life, several layers of armor, missile launchers, appropriate missile fire controls, missile magazines (unless you are using box launchers), and an active scanner sufficiently long ranged to provide targeting data for your missiles. (Tip: The Missile fire controls get the same range as an active scanner when they are 1/3 the size.)
2.) You probably want a combination of missile PDCs and ship squadrons, if you can swing them.
3.) That is totally dependent on your technology and on your doctrine. Generally, you should always be using the highest multiplier possible on your missile engines, and be using between 50-60% of a missiles size for the engine.
You can fill the 'short range missile' role with an Anti-Missile Missile design for now. AMMs are size 1 missiles with strength 1 warheads designed to hit other missiles. They need strong Resolution 1 sensors and fire controls. You will only need a minimal amount of fuel, perhaps enough to get it 10-20 million kilometers. For a long range missile, try size 4 or 5, and give it proportionally more fuel so that it has a much longer range.
4.) That's completely a matter of personal choice. I would suggest doing both
Survey ships with jump engines are much easier to shuttle around, and you can always use more jumpgates.