Welcome to the Pelican community! What is your BMW year/model? We have some great E90 tech articles that can be helpful here:
BMW 3-Series E90 (2006-2013) Technical Articles - Pelican Parts. For the oil change, you will want to raise the vehicle up so you can access the oil drain plug.
Here are the articles you'll want to view for your projects:
Valve cover replacement DIY:
BMW E90 Valve Cover Seal Replacement | E91, E92, E93 | Pelican Parts DIY Maintenance Article
Oil filter housing replacement DIY:
BMW E90 Oil Filter Housing Gasket Replacement | E91, E92, E93 | Pelican Parts DIY Maintenance Article
Eccentric shaft sensor DIY:
BMW E90 Eccentric Shaft Position Sensor Replacement | E91, E92, E93 | Pelican Parts DIY Maintenance Article
Take a look at them and they should help you determine in what order you'll want to do them.