How many drops needed and could it be use for continue use?
it depends on the concentration of your lugols, and the suspensions in the water - if it is unfiltered with particles or worse, cloudy? It'll take something like x2 or more. I think it's 1 drop 10% per clean liter, or working from that number depending on lugol concentration and water quality.
I'm not really worried about short or mid-term use. I suppose you learn to gauge not to put too much, and as you wait for the water to sit the iodine should react with most of the materials in the floaties and precipitate, or at least denature the moleculas etc. I'd hope that most of it precipitates, and not much would end up bio-available to you and affecting your supplementation. Either way, I currently supplement at 1 drop 7% a day, I guess I'd just stop using it for separate supplementation if I already used some for purifying the water.
I'm really not sure about that last one, and it's a good question. Does iodine that works toward purifying the water still count as part of supplementation? Does most of it precipitate out, or do you take in the denatured materials, and if so, do they remain bio-available? It's something I now want to learn :)
Edit; Worth mentioning is that if you plan to maybe purify water with iodine, make sure that you find iodine-safe materials for your water countainer. You don't want to have iodine-rich water leeching metals off glass, or all types of petrochemical garbage from plastic, while the water 'sits to purify'. You might need to look into it!