Unlocking, (aka Rooting/Gaining SU's/Administrator) void's your phones warrenty until you degrade to the stock then upgrade via your phones and carriers apporved ROM's. Rooting a phone is easy as long as you follow the guide, but the hardest thing to do really is downloading the Android SDK, and APT for ADB Batch Files. Just make sure you read all the documentation!
P/S: Some phone's, now, do not need the Android SDK so as I said before, READ ALL THE DOCUMENTAION!
Android SDK: http://developer.android.com/sdk/index.html
Java JDK (For the Android SDK, as IDE): http://www.oracle.com/technetwork/java/javase/downloads/jdk7u9-downloads-1859576.html
Android Repo: https://dl-ssl.google.com/android/repository/addons_list-1.xml
(run as Administrator/SU)
You really can choose any Custom ROM you want, but a good place to start is: http://lifehacker.com/5915093/five-best-android-roms
Any more information on technical aspects of your Custom ROM installation you can ask it either here, or on the XDA-Dev Forum more for Android phones.