1. I use this phone every day plugged on my hi-fi system and i've never seen an headphone icon :D I think it's normal. 2. The exclamation mark in lolliop is equal to grey signal icon in android 4. If the exclamation mark appears, there is a problem with google services and probably you won't receive push notifications. Did you stop any system services?
This is the best ROM for this device. You didn't describe your problems clearly.
There could be a lot of reasons if your phone starts to lag, e.g. a new application or malfunctioning app is installed. Usually a reboot solves al problems :D
Our device has only 512MB RAM and around 100MB is reserved for GUI. RAM full is not a problem, I suggest you to read about Android memory management to see how it works :)
As @flea997 said, your the only one to say this rom is not good :D
Battery drain is due to Google Play Services, it's not H3ROS fault :)
You have 3 ways to solve:
1) Uninstall Google Play Services (but you will lost a lot of features such as push notifications)
2) Disable some service of Google Play Services, but be careful because you can face many stability problems
3) Buy the full version of greenify (around 2-3 euros) and greenify it. I think this is the best solution: fast and simple and you won't have nightmares in the night :D
I just wanted to say that you cannot see the difference if the clock speed is 1008MHz or if it's 1046MHz while you're using you phone :D
The answer to your second question is simple: RAM is 512MB but you can only use a part of it because another part is dedicated to graphics unit :)