Welcome to the forum.
1) I think the common consensous and from what I have researched is that it is best to have a diversified collections of gold,silver and maybe platinum to try and limit your exposure if there was a sharp decline in the price of the percious metals. One thing to remember especially if storage space in limited is that silver takes up a lot more physcial space than gold for the equivalent value. At current spot price a 100oz bar of silver (which weighs around 2.8kg) is roughly worth the same as a 1oz gold coin that can fit in your pocket.
2) Personally I would go for a mix of both. The premiums tend to be better on the large bars which means that 100oz bars will cost less than 100oz of coins. So you get more bang for your buck. This is a generlisation though and there are deals to be had. One thing to think about is what is called the exit plan. If you needed sell your silver in a hurry would there be many buyers for large 100oz bars or would there be more buyers for lets say 10oz of coins but selling to 10 different people. I am not sure what the precious metal market is like in Israel but something to bare in mind.
I am sure there will be some more experianced forum members who will be able to go into more detail. I am still fairly new to this myself just though it might help.