Welcome to Silver Stackers
My advice would be to find out what your primary reason would be for stacking. E.g. collecting silver coins/bars etc, hedge against economic down times or just a diversification of your investment portfolio.
For example you would be looking for 1/2oz and 1oz coins/rounds/bars (hedge) and 10oz and 500gram bars (investment) that are lowest over spot you can find. Basically called generic silver. Why generic as it buys you the most oz's of silver for the same fiat currency. This is especially great when you just start as it gives you a boost to build a hoard.
If you do choose to collect then you want think of various types (bullion coins, proof coins, minted bars, poured bars, hand pored in various sizes/shapes by professional companies and individuals) of coins/rounds and bars and preferable without scratches, milk spots etc. and get capsules, special gloves to handle and store them.
Personally I'm a silver is silver person and just use it as it partially as an hedge and partially as a diversification of my investment portfolio.
What you get in size/amounts etc is based upon your personal situation.