yes you can root it, if you just want root for now use CF-Root, this will also install Clockwork Mod which will then allow you to perform Nandroid backups before you attempt any use of custom ROMs, its very important that you always do a Nandroid backup before any attempts to flash anything related to Kernel modifications.
It is nearly always possible to access Clockwork Mod and restore the backup should something go wrong with flashing, Unlocking can be done once the phone has been rooted and there are currently 2 free apps in the market that can do it, one is quite safe to try but the other uses a much more dangerous method to achieve unlock and I would not advise using it unless you have a Nandroid backup as it could damage the data held in a folder called /efs, this folder contains crucial encrypted data related to your imei number and other things, if this is corrupted you will end up with a very expensive media player as the phone function will be useless.
For a good stable first ROM at your stage I would recommend this
Code:
http://android.modaco.com/topic/344911-19-aug-gr5-xxkh3-modaco-custom-rom-for-the-samsung-galaxy-s-ii-stock-stylevanilla-with-online-kitchen/
There has been a new version of this ROM just released but it is still a work in progress so not ideal for a noob.
At the moment you are better staying away from any ROMs on XDA but there is lots of useful info on there but it can be very confusing to a beginner.