I've been IV'g for 18 years, but it wasn't daily till 10 years ago. I averaged 6-8 shots per day (I stopped last month and am near zero on sub). I used the two big veins in the crook of my left arm (Lazarus [cephalic] and Old Reliable [basilic), plus one on my right when the boys needed a break. I saved a smaller one on the right for blood tests, thankfully. I promised myself I would stop when they ran out and not go to the hands. I broke that promise about two months before I stopped. That scar is now fading.
My veins are very scarred, even though I used new needles and always held down the injection site with tissue for about five minutes afterward. Also, I alternated the site as much as possible, even if it's just a mm or two away from your last shot--you can tell when the area gets super sore that it's time to move onto a different area. On my (formerly) big ones I had to go about an inch down away from the crook of the elbow just because the crook became way too scarred to use. They're both still viable now that I've healed a bit, but I think a big miss would shut down even Lazarus.
The extent to which you will scar depends mostly on your technique but also on your body's ability to heal. My ex and I had the same routine and she didn't scar like me. I have a lower white blood cell count so don't heal as well as some.
I do know people who have a terrible time in hospitals getting a vein to come up and have to use the one in the chest. I'm glad I'll never be in that situation. However, I think I will always have the purple scars on my arms unless I get surgery or something. Long sleeves for me.
I never used micron filters and wouldn't know how to find one in Winnipeg. I used a third of a cigarette filter--I found that certain brands never gave me cotton fever. The last five years I IV'd oxy which has less gunk that ms contin (or dillys, which we used to "shake and bake" i.e. grind the pill, pour into the needle, suck up water and bang all the crap into the arm. imagine. thankfully I didn't do that more than 10 times or I'd have serious lung problems).