Just buy a decent panel filter instead standard air box is well better unless 350hp is your ballpark, then if your on a budget get an open source map should only cost about 200-250 quid. on the topic of can you replace up pipe with out map I’m not sure some say yes some say no. A good starting point is fuel pump panel filter cat back exhaust and map makes a difference. Of course decat or sports cat down pipe are options aswell. Again this is what anyone who mods/ maps Subaru’s will tell you.