Going by the product info on your first sylmasta link, I would go for the first product listed. I wouldnt bother with the clear resin (the 2nd item), that would be more usefull for water in diorama's.
Just follow the instructions and the mold making should go ok. Like wise with the resin. Expect failures in the casting, you will soon work out why resin kits and extras are priced the way they are.
Before you do any mold making or casting, raid the local pound shop for a box of cheap disposable latex surgical gloves and a stack of plastic cups to pour mixtures into. You will go through them like no body's business. And if you havent got one to hand, get hold of a fair sized tray, to do the mixing and pouring on. Your bound to over fill the mold, so expect it to over flow, the use of the tray will soon be self evident.
hope that is a help