The whole discussion regarding collecting, stacking and liquidity is interesting and there will be differing views. I, too, am relatively new to the the world of physical PM, but have some thoughts:
1. Silver coins are nice, but I question the real sense if truly stacking. Are we really thinking that at some point we would use them in exchange for goods and services? Is there a high risk that once you start buying coins, the greed monster kicks in and, where you may have deliberately said "split between Brits and Maples" only, it soon turns into Kooks, Krugers (ASEs if someone is selling cheaper than normal) etc? Also, they tarnish!
2. One common maxim is that you watch the gold versus silver ratio. Whilst the number is deemed high, as now at a little under 80:1, you buy silver. When that number drops, perhaps to 50, you sell the silver and buy gold. If you follow this, then why not just buy manageable bars (10oz, 250g to 1kg)?
3. Everyone considers different factors when discussing the future of silver. My hope is that any manipulation of the price is relaxed/stopped, but I am also conscious that something seismic may catch us all off guard as Govs could introduce measures to control the price in line with a growing industrial consumption (Indeed, something sooner may happen if the bank exposure is truly understood). If the former, and the aforementioned ratio rebalances, the stackers are quids in with multiple 100% ROI. If the latter, we could all be sitting with dead ducks and wishing we just bought gold.
4. Sovs v Brits. Yes, Sovs theoretically are easier to sell on at a time of need. If you are in a time of need, is £360 or £720 going to be sufficient?
5. If saving for the future, ergo the long investment, then the common cry is the cost now and the premium is less important (than if you are flipping). If you are saving for the future, perhaps you are investing a set amount per month, then surely it's best still to buy the highest amount at the lowest premium? The aesthetics and heart needs to take a second place to a more business approach. Of course you can go down the more specific long term investment, buying a rare coin or sets of highly graded or similar, but that is another game and not stacking.
6. Consider the current CGT and VAT rules.
7. A couple of final thoughts:
a) Collecting coins, gold or silver, can be addictive. Don't get attached
b) There are many sovereigns; there are many different Au and Ag coins. Limit your horizon
c) Consider storage space and insurance
d) Talk to people that have been in this market for sometime. I have found people on TSF to be extraordinarily kind when sharing advice and thoughts as well as services
7. Last point is that I wager that what you are planning now, your strategy, will have changed within 12 months.
All the best with whatever you do.