1. If you where buying 1 miner today which would it be to have best ROI without electricity cost ?
2. Will i need something in addition to mine except miner and PC ?
3. Average how long it will take to get ROI ?
1) Well if you have "free" electricity anything is on table. Just look as some take 220/240 and you might have 110. You will need to look into this. Also how are you getting free electricity? Most someone is footing the bill
2) Proper cooling, area depending on noise, right electricity, internet, etc
3) At this point there is no average. It is very different for different people. Look into bitwisdom and do some calculations.