My two cents, my doctrine is almost completely different from Jumpps in every way.
I tend toward size 4 anti-ship missiles but 4-6 should be the range you aim for. Anything smaller than 4 and its hard, especially early on, to make a good anti-ship missile, anything larger than 6 and its going to be seen sooner (resolution 1 sensors see size 1-6 at the same time with larger missiles being seen farther out).
Most of my fleet uses the same engine, a 5 HS one but that is completely personal preference. It allows me to have several engines, especially on my larger ships, so as my ship gets damaged its a smaller reduction in speed per engine destroyed, which will happen. The downside of this is fuel economy (each HS of your engine saves you 1% fuel), and 5 damage will destroy my engine whereas Jumpp's engines will take 50 points of damage before being destroyed.
I don't make my ships exactly the same size, I use several different designations of ship and almost all of them are under 16,000 tons. My cruisers tend to be in the 5,000 to 10,000 range depending on what I am feeling, and generally I have at least one class smaller than that at about the 3,000 range and a battleship 15,000-25,000 with a carrier 20,000-30,000. Each ship class and to a lesser degree each designation has a specialized role to play. Again this is mostly personal preference, but that is something you will develop as you play the game.
I mostly agree with Jumpp on sensors, but again we differ. In the past you could get away pretty well with sensors with resolutions 1, 20, and 200 though putting a sensor at resolution 100 was good and larger also didn't hurt, but I have found that those are good base sensors with others being added to defeat specific enemies. With the addition of fighters for NPRs in version 7.00 you want a sensor resolution 10 for fighters. As for size you want your standard ships to have size 1 or 2 of at least your larger one if its a ASM ship or your smaller one if its an AMM ship (or both if its a mixed role ship). Generally I also make a size 5 or higher for an AWACS type ship.
As for range, that is based on the size of the systems you are finding (although 20 billion km is plenty for Sol) and how long your ships endurance is. 30-40 billion km is generally fine but there is always exceptions.
I don't go with reduced rate of fire (ROF) launchers and am of the school that you should get as many salvos out as quickly as possible. You should get rate of fire 6 as fast as you can because that puts your size one launchers (your AMMs) at firing every 5 seconds, which is the quickest it can. Now this is also one of the reasons behind my size 4 ASMs. At rate of fire 6 a size 6 launcher fires every 30 seconds, a size 5 fires every 25 seconds and a size 4 fires every 20 seconds. Now going on to the next tech size 4 and 5 stay at 20 and 25 seconds while size 6 drops down to 25 seconds so at this tech there is no point to have a size 5 missile since size 6 will have more stuff and fire just as fast. The next tech level sees size 4 launchers drop to 15 seconds, size 5 goes to 20 and I don't remember if size 6 goes to 20 or stays at 25. Either way, starting at the size 6 tech level the tech starts costing a lot more and not every level brings your launcher fire rates down but size 4 is at a respectable fire at this point.
Another thing to consider with size, beyond speed of missile, chance to hit, damage, and as we just talked about rate of fire, is magazine size. If we have a magazine that can hold 20 MSP, Jumpp can only hold 4 missiles while I can hold 5. This keeps up through the size of the missiles with my size 4 getting 5 for his every 4. As long as my speed and to-hit chance is good my higher number of missiles and greater numbers of salvos in a given time I should be able to get more damage than him. This boils down to the age old argument of is it better to hit more often for less or less often for more?
As for speed of your ships and range of your weapons, I have this to say. If you have a longer range of your weapons but your sensors and fire controls can't match that range its worthless. If you have a longer range with fire controls and sensors to match then you fire first. If you have greater speed you dictate the range in which the battle takes place. If you have a greater range and greater speed then you can keep out of their range but within your range and fire on them with impunity. The larger the difference in speed and range you have over them the bigger mistakes you can make before it starts costing you.
The biggest problem with beam weapons is your enemy WILL have greater range than you, there is no way to change that. So to even have a chance you must either surprise him, take away his range, or be able to close to the range in which your weapons work without dying. Surprise can happen either with extremely high stealth levels (pretty close to not worth it) or from jump points. Jump point defense and offense also takes away the enemy's range as most jump point battles start within 200k km which a fairly low level beam can do. Another thing that takes away his range is electronic warfare, ECMs to be exact. You must have a speed advantage or no matter how close he must be to attack you he will be able to get out of your range and stay within his. The last major problem with beams is you are going to have to weather a large number of salvos while closing the distance but you can use your offensive weapons as anti-missile weapons while you close.
