At Town Hall Level 4, you will get:
- your 2nd Archer Tower
- your 1st Air Defense
- two Spring Traps
- one Gold/Elixir extractor
- one Barracks
Level 4 Town Hall Base Design
Don't forget to build the Air Defense tower. Although you would not face lots of air attacks, it's good to build all the available buildings and defense structures.
Upgrade as fast as possible to Level 5 Town Hall so you get your first Wizard Tower which deals splash damage but don't forget to max everything before going to Town Hall level 5.