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The difference for both of these units you can see it here:
Both are Rock Canyon units and they are very similar, the difference will be with graphics, the NUC5i5RYH supports the Intel® HD Graphics 6000 and the NUC5i3RYH supports Intel® HD Graphics 5500.
1) I honestly have no test connecting and reconnecting the cable form HDMI several times but I would say you will not have any problem. I would recommend turning off the unit first, unplug it and then disconnect the HDMI every time you do it just to avoid any issues.
2) You can find locations in India at:
3) Amazon is very reliable website to purchase this product; this is a very popular website in USA to purchase Intel products.
4) Please see the RAMs tested with these units at the following link:
5) The Kingston RAM KVR16LS118 will work ok for these units because is on that compatibility list.
6) For M.2 SSD you can check to compatibility list here: