There is a lot of ground to cover from your questions. When you ask a question concerning a transceiver radio, antenna, amp, etc.; it often leaves you with more questions.
First advice I'd give is to learn more before installing an amp. It can dramatically change your system. If things aren't correct you can end up with smoking equipment that no longer works. Antennas set up is going to get you heard more than power. I know you are running your radio in a mobile, but just for example. Take a 100W radio with a mag mount mobile antenna vs. a stock radio with a 1/2 wave antenna 36' in the air and the stock radio will probably out talk the big radio.
I think the best advice is to get your antenna right first. Being new, I don't think I'd run out and buy an antenna analyzer. Get a decent SWR meter and that will get you started. If you decide that radios are a permanent hobby, then you may want to invest in an analyzer.
To understand a tune up on the radio, you really need to know how the radio functions first. When I bought my first two radios, I had them tuned up because it sounded like I was going to be the king of the air. The guy that owned the shop just opened up the radio and turned everything to the max. The radio sounded bad and wasn't functioning properly. An improper tune can be deceiving. You can see more watts on the meter, and still have less performance than a stock (unturned) radio. Once I learned a little more about how the radio works, I was able to find a shop that was able to right my radios and now they sound good and perform well.
When you do get an amp, I would start with something small. Maybe a Texas Star DX250 or an RM Italy KL203. You can have variable power added to your Cobra 148 so you can operate it like normal with the amp off, then turn down your power for use with the amplifier. If you feed the amplifier with too much power from the radio, bad things start to happen. Many times you kill the amp.
