How to fully maintain a bicycle myself?
Park tools publishes a book on bicycle repair and maintenance: Big Blue Book of Bicycle Repair.

Park also has a YouTube channel and Repair Help Articles.

Global Cycling Network has some maintenance videos on their YouTube channel

Performance Bicycles has maintenance videos on their YouTube channel.

Also MBR Magazine YouTube channel.

For some good places to start, try:

GCN's 5 Essential Bike Maintenance Tips

GCN's The 1 Hour Tune Up - How To Make Your Bike Feel Like New

MBR's How to Carry Out Basic Mountain Bike Maintenance