- Do you recommend holding it inside?
I strongly advise against it. Pines belong outdoors.
How often should i water it? Now i do it almost every other day.
Depends on various things like your substrate, the weather (it needs to be outdoors). Look up the care guidelines for pines (top of the page).
What is a good information source about this type of tree?
Google. Search 'black pine bonsai care'.
You'll find lots of sites, some better than others. Try and find real in-depth guides.
Also look on Youtube for movies about black pine bonsai. Learn about decandling / candle pinching before you do anything, and learn the difference between single-flush and dual-flush type pines.