I'm considering using a water filter just prior to bottling in order to filter very small particles. But would that also filter the yeast and prevent fermentation in the bottle? What micra in what stage is better for filtering? Is using filters good practice at all?
There are several different homebrewing filters out there. 1 micron and 3 micron filters are most typical. It will dramatically reduce the quantity of yeast getting passed to the bottle so you may want to pitch some krausen with your priming sugar if you are going to ferment in the bottle. Not too sure if it really makes sense to filter if you are going to do bottle fermentation.
Depending on filter size, it could filter out yeast. Also, unless you have a closed filter system pushed by CO2 you will oxidize your beer. I used a filter for a little while but stopped. I found it to be a PITA for not much benefit and also found that it seemed to strip body and flavor from the beer.