The conversion to JAR topic has been covered ad nauseam on this forum, relevant information is abundant, assuming that you are eligible for work in Europe.
Concerning your questions:
How long does it usually take to study and get the written test out of the way? Since you are a holder of an ATP you can be exempted from taking ground classes, which is probably not recommendable since the writtens are hardcore (14 written exams)
How much flying training does it take? Up to the school really depending on your proficiency. Pretty sure it has to be on a ME ship.
Will I need to shell out for an IR rating to be eligible for a job? Most likely yes if you are aiming for the Offshore since nowadays Operators don't sponsor IRs anymore.
Have you heard of any guys from the US coming over and working in Europe? Expect from dual citizens or US citizens married to EU citizens, not really.
To sum up: If you are aiming for the Oil Offshore industry (Based on your money comments) and are eligible for work in the EU, you probably ought to get in touch with folks like Bristol Groundschool, Caledonian or GTS and get some quotes, ace those 14 exams through the UK CAA (Despite their flaws probably the most efficient system to go through in JARland in order to obtain your Certificate), do a CPL ride on a piston like the H269, convert your FAA IR onto a JAR IR while it's still feasible (Not much time left) and ideally if you have 500 hours on a frame like the 76, 365, 139, 92, 332 or 225 transfer the type onto or you JAR license and should be in a good spot for a job interview
