1 The degree of certainty- there might be conditions that need to be met in the first or even no possibility of it being done.
2 You don't have to- you can use the present for facts and things that don't change or when something is known to be the same. Here, I'd use the present if Sam's being alive were important at the time of speaking- if, say, there had been an accident and Sam was in hospital. At a distance from the event, I would probably change it.
First person: I/we
Second person: you
Third person: he/she/it
Person - Glossary Definition - UsingEnglish.com
By the way, that's possibly a bit of an old grammar book- the rule doesn't hold true in the US, where 'shall' isn't used much at all, or the UK, where 'shall' is used, but rarely in that way. In a discussion here, I read that the rule is still taught in South Asia but don't know how widely it is used.
4) Playing with, fiddling, adjusting, especially mechanical/electronic things
- For Teachers