There's a pretty steep penalty for murdering someone (in a nutshell, it exposes their own character to getting possibly murdered for a number of days afterwards) so it's unlikely (but not impossible) that someone encountering you randomly would permakill you because you would pretty clearly be a new player and there would be little to nothing to gain from it and no bragging rights either. They may KO you and steal a few things, but that's not the end of the world.
Getting things stolen from your settlement though is an entirely different story. IMO, just chill and wander and enjoy Salem for awhile and don't stress about hoarding valuable items or even building a base at first... Just work on your character and check out abandoned bases and look for a nice place to eventually settle.
Once you do want to start defending your things, this is a nice guide on fending off thieves and what you should focus on in the beginning as far as protecting your assets goes:
viewtopic.php?f=5&t=12582 It's pretty old (a bit over a year) but from a quick skim it still looks relevant.
is it worth purchasing anything in the store to assist in the starting out phase? or is that best left for once you are firmly settled and have a firm base of operations with friends to back you up?
Yes, definitely don't buy anything expensive from the store until you have a base. (nub pack is pretty useful though, yeah, but you can get by without it too so you might want to spend that $5 on something more advanced instead) Or if you do buy things, make sure to keep them in the postmaster (where you pick up store things and gifts from the devs) until you're sure you can keep them safe.