There a ton of decisions to be made when making a system. Start with the decisions that have limitations, Roof space, needs, room for batteries, budget and what's available to you. These are the things you work around with decisions like MPPT vs PWM, series vs parallel, 12v vs 24v, what controller, what batteries, etc. etc.
Each decision you make will affect or limit another so don't make any until you have a handle on the basics so that you can make choices that work well together.
We all look at things differently because our individual set of circumstances require different approaches. Controller efficiency and heat are important to me because our system does little battery charging and a lot of acting like a generator. It's expected to run at full power running things like a small air conditioner with out depleting the bank. So more amps and a cooler controller is a big thing for me. It's just one of the decisions I've made and am still making balancing the whole system out.
