Question How many fans do i need?

That all depends on the case and what MB, CPU, GPU you have.
I personally have 2 front fans and 1 side panel fan as intakes.
And I have 1 rear and 1 top fan as exhaust and that keeps my mid-tower, Ryzen 5 2600 rig very cool.
IMO, more fans are always better as long as the are properly positioned and controlled.
 
Depends on quality of air flow in the case and components you have installed. I have a Corsair Vengeance Case that is huge and lots of room. Most cables are off set to side panel. I installed 6 fans plus heat sink fan. Temps run about 22 Celsius. Noisy but cool, CPU likes it cold. If you install an SSD instead of standard hard drive it will reduce temperature. Computers worst enemy is dust and heat. I know most will say mine is an overkill but different strokes for different folks.
 
My criteria for a good case:

It must hold your parts. A ATX motherboard fits in an ATX case but not in a M-ATX case.

I want at least two 120/140mm front intake fans that have a washable filter.
That will supply sufficient airflow to cool a hot cpu and a good graphics card.
One can always increase the RPM of intakes to provide more airflow.
If the front intake is the only source of fresh air, your parts will stay cleaner.

I like air coolers. 160mm will be sufficient for the best of them.

Lastly, and most important, the case must look good to me.
Bust your budget for a case you love; it will be with you for a long time.