My arrow stock hasn't gone below 300 since the tutorial area after at least 70 hours. The maximum I had was just over 600 arrows. And I use them for almost everything. I collect the arrows that enemies shoot, arrows in boxes, in barrelsand in chests, arrows that enemies drop when they die etc. I also try to always retrieve all arrows that I miss with if I can. No arrow goes to waste.
I never buy arrows in TotK since rupees are harder to come by. In BotW I'd constantly buy arrows, that was my main source of normal arrows in that game. I always had 100-150 of each arrow type except for bomb arrows which I had maybe between 50 and 100 of.