In terms of the full-size Comex contracts, as of today's close the correct hedge ratio for currency-adjustment is 1 Gold versus 1.3 Silver. In terms of volatility weighting, 1:1 is just about spot-on correct. As far as spreads go in the metals space there are much better ones that are more worthwhile to pursue IMO if you can get access to the LME 3 month contracts. I have a couple of clients who are just printing money trading the LME. The reason I am lukewarm about Gold as far as spreads are concerned is the directionality of the spread with the flat price Gold future. There is a substantial 'flight-to-quality' order flow component in Gold that introduces cointegration into the trade, and in my mind a trader experiences delta risk because of that factor. I'm not saying it's a terrible trade, my point is that there are much more fertile spreads combinations in the metals space.
For the currency adjustments, look at the notional value of the contract at it's current price level (price x tic value). For the vol adjustment, look at each instrument's volatility - I tend to refine the modeling timeframes based upon my planned trade holding period, with 20 day studies being the minimum. There is some proprietary art here, but you certainly get the gist.