oil leak

That would be a leaking valve cover gasket. Replace that and you should be good. Remove the plugs and let the oil drain into the cylinders. It will smoke a little on start up but it will burn it off quickly.

There are o-ring type gasket that go around each spark plug well in the valve cover gasket. This is a situation where oil tends to also fill the plug well around the spark plug where it goes into the head.
I am including a diagram of the valve cover so you can see where the spark plug ghaskets would go around each spark plug.
You just need to replace the valve cover gasket if this is the case. It should come with the spark plug o-ring seals.

If you think it might be something else or you have any more questions, please let me know and I will get back to you ASAP.

Does the process of changing the head gasket involved the timing belt in any way

Hello.

Yes. On this particular vehicle, the timing belt must be removed in order to replace the head gasket.

Let us know if you have any other questions!