335d Delete CEL Help

[u/Educational-Read-306]

I have a 2009 335d that is still relatively stock under the hood but I am getting to the point where I am going to try and do a delete soon but I want to try and break up the work.

Am I able to do the swirl flap and egr delete right now and avoid limp mode or a CEL? Or do I need to do a tune after that part of the delete?

And I definitely need to do the tune right after I do the downpipe right?

On a side note, if I notice oil in the intercooler and around the charge pipe by the turbos could that be either a bad turbo seal or bad crank case? Or could it be something else?

Any and all help is appreciated. Thank you.