What model heads are they? I just had that problem with my Hunter PGP rotors. They Have been in the ground for about 9 years. They have some repair parts available but considering the age I just replaced them. Before you do anything take the heads apart and flush everything out with water. Sometimes debris can get into them and cause a leak at the seal. If that doesn't work then replace the bad heads.
Rainbird ESP modular controller will do what you want.
You should have good head to head coverage (overlap) on spray heads as well as rotary heads.
Hunter PGP rotors. A couple of them are leaking where the top is threaded onto the body. I took them apart and cleaned everything but it didn't help. I saw a replacement seal/spring seat kit. Is this the kit that I need for this problem? Is it worth it to rebuild them or just replace?
I would not use a snap tee. Dig out a large enough area to work with and do it right with a regular tee. You'll never regret doing it right the first time.
I would not use 3/4" lines. Use 1" line for everything. The only reduction in size should be at the individual heads. There are lots of options for setting up the heads. I prefer to use swing (funny) pipe for the connections to the heads. Some people use risers that are cut off at the height that they need them. There are also saddles that pierce the line and make the connections. I prefer the flexible swing pipe because I have had to move heads at certain times due to lawn or garden bed changes...
How did the city determine what the psi was at your house? You can use an inside faucet, preferably one in the basement with no restrictions on it, to get a rough idea of the gpm with a 5 gallon bucket and a stopwatch. I would get a pressure gauge and get a reading for your actual pressure. If you do in fact have high pressure then you will need to install a pressure regulator which is not too difficult.
If you set up the drip line with the emitters built in you are not limited to a straight run. You can install tees and run some short runs off of the main drip line around specific plants.
Whether or not you need the outside meter depends on your water department. I have an outside meter for the irrigation and the outside spigots. There is no monthly charge for the meter only the cost of installation. We pay big water bills in my area and the majority of the charge is for the sewer charge, so with the outside meter they subtract the sewer charge from the second meter. I couldn't afford to not have one but for you it depends on your jurisdiction. The 10-12 gpm that you have with 70...