Over filling is bad news for oil seals and creates excessive pressure in the engine. Firstly drain some oil out, you could just remove the oil filter to do this depending upon how overfull it actually is. Don't think it would be a good idea to run the engine until you do.

Take the charge carrier pipe off and the boost pipe to the turbo and see if there is oil in each. If so it could be your turbo oil seals.

Smoke on overrun suggests worn valve guides, stem seals or turbo oil seals. Do the above first then post your findings.

Stem seals is easiest if you have the tool for the job (less than £10 for one) but if you drop a valve collet down a hole in the engine the sump will have to come off to recover it. Best to block all holes with rags first.

Valve guides is a head off job and give it to a pro to do. You will need to budget probably £100 to have it done plus new head gasket and head bolts (about £60).

Failing that the turbo needs to come off to be replaced so you will need to remove the bumper, rad and intercooler to get the best access. Obviously this will be more expensive route (approx £500 for new turbo) so make sure your fault diagnosis is correct first.

You may be lucky once you remove the excess oil the problem will stop but you may have damaged something already.