It doesn't hurt to get rid of the up-pipe. Yes, the cat can break apart potentially leading to turbo failure.
Yes, removing the banjo bolt filters is something that should be done. Another potential turbo failure.
Intercooler leaks are common, starts to leak where the plastic end tanks are crimped to the core.
Oil consumption is a normal Subaru thing, but there are things that can be done to reduce it. A good quality and heated AOS is necessary on every turbo Subaru IMO. Yes you can top up the oil between changes, but that doesn't change the fact that you're re-circulating a ton of oil vapour back through the engine. When this recir'd oil vapour combines with your fuel mixture, the effective octane rating is lowered.
My suggestion is to have a pre-purchase inspection done before buying a used car. If budget allows, also perform for a leakdown / compression test. This assures you the actual mechanical condition of the vehicle, and gives you an idea of engine condition as well.
