does it remove bacteria

Yes, they do remove bacteria and viruses.

How many gallons of water does a new 28oz bottle filter?

They have a filtering capacity of 100 gallons.

I need to know the difference between the 38 oz extreme flip you filter and the 20oz pink extreme filter going to be in wilderness situations. Thank you

The 28 oz and 20 oz filter the same. The 28 oz holds more water and is more durable than the 20 oz. For camping, hiking and as you state wilderness I would recommend the 28 oz bottle.

Can I use well water in a developing nation? How does the add on ph filter work? Can I buy replacement filters for this? I spend up to 9 months a year in Liberia West Africa. Is there also an extreme picture model.

Yes, you can use well water. You would just purchase the Ph filter and use it in the bottle. Yes, you can buy replacement filters here is the link to them. No there is not a pitcher with the extreme filter but we do have a pump.

Seychelle Extreme Replacement Filter

Seychelle Pump Water Filter

Can I use rainwater in bottle?

Yes, you can use rainwater or water from a lake or stream.

I was using this one everyday, at the gym and out and about. I drink the filtered water from the pitcher at home. Is this better than the ph20 Pull Tops. i see it is more expensive, but is it better for daily use?

Yes it is a lot sturdier, It is not a ph filter but you can also put the ph filter in this bottle also.

How much fluoride does this remove?

They reduce up to 90% of fluoride.