regarding issue 1, a list of all stocks on T212 is here with the values you need (ticker, ISIN, exchange)
note: this was produced by finki, about a month ago in this thread…
you should be able to just concatenate the exchange with the ticker to get the google finance input, (eg: Map London Stock Exchange to LON, then concatenate to :NG to get LON:NG) This spreadsheet mapping will get outdated however and how to keep this up to date would be another issue…