If I play squire can my alternate character use my squire’s refreshment table.
If can, Does it need any condition? Like I have to create party first?
I want the play squire to buff my own alternate character but I want to make sure first that it is possible or not.
Yes, you can. 
so just relog another character thats it? or do i have to create party first?
another question what make more profit between repair vs weapon buff
Yes, relog (change character). Create party only to use warp (warp to base camp).
Not sure this is a bug or intentional (since ktos patch), but if you offline too long or relog too many times, your camp will disappear even you just setup your camp 30 minutes ago. In this case, setup camp only if you want to stay for a long time in game.
I have armor maintenance to support my main.
Personally I think both sucks at silver making. Better solo dungeon 145 every day.
The camp and food table will disappear if the map population drops to 0 regardless of whether or not it had time left. To avoid this, either put an alt on a second computer on the map or pick one that has a high population at all times.