If supposed I upgrade after 6-12 month to Ryzen 2400G or i5-8400, than will this GT710 good or GT 1030 2GB GDDR5 will be more useful at that time
In case of Ryzen upgrade, both GT710 and 1030 will not be much of use because processor itself has better performance. For i5-8400, GT 1030 would be little bit more useful than GT 710. But again, basing your current purchase on future upgrade which are not very certain, is not a good idea IMO.
Again GT 1030 would perform better but what usage ?for i3 - 6th Generation which will be good (as after year I may land my Graphic Card to my Nephew who is using same system and I don't think he may wish to update for 3-4 more years)