Sodium (the half of salt) is hydrophilliac (It attracts water). In medicine, it has been a rule of thumb that "Where sodium goes, water follows", which explains the fact that your pee, tears, and sweat are all salty... Sodium and Water are nigh inseparable. So, to answer your question, yes sodium does make you gain weight. But it's actually the water that it attracts that contributes to the weight gained.
Yes. When you consume more sodium than the amount your body can take, your kidneys have to work extra hard. This build up causes your body to retain more water and fluids which causes weight gain.
It can make you bloated which can potentially make you gain a small amount of weight.
ya ofcourse they does espicially if the intake is more