This is just advice I have learned from friends , experience and reading after owning Subarus for the last 6 years. It primarily applies to turbocharged subnarus but I would apply the same logic towards an EZ30 or EJ25D powered car as I would with my EJ207.
What oil should I run ?
I have ran Castrol , Redline , Motul and Mobil 1 oils in my cars with over 100,000 miles and no engine failures due to oil. Most Subaru engines that suffer oiling failure are simply due to running low on oil so in that case it does not matter what oil brand you run but more so that you engine has oil in it and it is changed in regular intervals. If the car is your daily driver then a standard 5w30 or a thicker 5w40 can be used. 5w30 is the oem fill on the Wrx and STi but special editions like the S20X models suggested using a Motul 5w40 which I would assume is because the engines bearing tolerances are looser and the engines are expected to be driven hard. If you plan on tracking your car you may want to bump up to a 5w50 or even a 5w60 depending on your climate as those oil weights will take more thermal abuse than a 5w30. On my daily driver I run Castrol Edge 5w30 or Motul Eco Energy 5w30 and on the Wrx I run a 5w40 Redline or a 5w50 depending on what I am doing with the car. 5w50 Redline has held up extremely well on the track but if that is too expensive for your taste Mobil 1 makes a 15w50 that is much cheaper and that has worked well for friends.
The first thing to realize when stepping into tuning is that the oem ecu calibrations are a compromise of fuel economy , power , emissions and driveability so they are going to be imperfect to most owners. The oem supplier has to hit emission standards that are becoming increasingly strict especially in states like California and it is probably the reason why the EJ207 never was imported to the United States. I would suggest that anyone who is looking into tuning find an experienced tuner in their area and also learn how to datalog because if you understand the data that your engine is telling you and see that there is a problem like the ecu pulling a ton of ignition timing you can save yourself from a very expensive engine rebuild. It also would not hurt to have other people look at your data logs because a second set of eyes might see something you have overlooked. Also don’t be afraid to drive 2-5 hours away to have an experienced and reputable tuner work on your car as spending the extra $30 in gas money might save you $1000s over having some local bro flash your car with a base map he found on the romraider forums.