Dex speeds the cast time of spells (although I find it to be so minor I don't even notice it - but you can find youtube videos doing more detailed analysis).
There are good weapons for both Str and Dex, although IMO - for a new player, I think Dex weapons are a little easier to use. I found when I first started playing the Souls games that the Str weapons felt a little clumsy to use (getting used to them now and rather like them), where the move set / speed of the dex weapons (ie: Iiato/etc) felt pretty good.
I'd also probably focus on END before VIT - still keep them balanced, but find that End tends to help my survivability more than VIT. Depending on my play-through and how I'm feeling, I'll bump up the one that I feel I need the most.
END affects how much gear you can carry and get a decent roll speed (fast / medium / fat roll), you'll want to aim for at least medium roll, which is an equipment burden of 50% or less (ie: you can carry 80pounds of stuff, so your burden should be 40 or lower). There are a few items that can increase this - so I usually play around with 'the gear i want to use / the burden-increasing items I want to use / the END I need to keep at the roll speed I want'.
If you are thinking in terms of a 'SL120 build', a common rule of thumb most people seem to have is
- VIT/END to 40
- Other stats to meet item requirements
- Bump up your damage-scaling stat to 40 (diminishing returns after)
- Enough attunment to carry the number of spells that you want
If this is your first play-through though, don't worry too much about the 'perfect build', leave that sort of min/maxing/perfecting for your other characters (of which will level up and complete the game much faster than your first time).
