Good questions. I will try my best to answer them

1. If you get 1x8gb stick, your pc will still run, however your channel will bottleneck. Imagine a channel as in like a tunnel through which information flows. And behind the channel, you have a storage of 8gb of data. But no matter how big your storage is (even 16), your channel capacity will remain the same, means the info flow rate will remain the same. Now imagine having 2x4gb rams. Your storage is divided but remains the same, however now you have two channels which means double the amount of information flow.. thats why 1 stick is never a good idea. The motherboard i have recommended has 4 RAM slots. So in future, if you like to upgrade to 16 GB RAM, you can easily do it by purchasing another pack of 2x4 gb sticks.

2. About the smartcash, yes i am still holding with no intention of selling it before it hits 1$ per piece.

3. About steem vs smartcash. Its very hard to compare since it is based on many factors like price of steem and smartcash. Also, your reward in smartcash on 25th of each month depends on how many people in the world are holding their smartcash in their official wallets. Lets say if today the entire population takes out their smartcash from smartcash wallets except you, you will be the only one who gets the entire reward which will be in thousands of smartcash (if not in millions). Similarly steempower is only beneficial if steem has high price because the higher the steem price is, the better vote value you will have. But thats an interesting phenomenon on which i would like to create a post in detail. However, if you take only current scenario between smartcash and steem, i believe having steem is more beneficial right now. I hope it clears alot of doubt in your mind. Much blessings brother..