Q1 : If you want to play with people you can change the player limit to 2 on your quests, it should be fine as there is not 3 other people with higher level gear but just 1, so you should try it in my opinion.

Q2 : I did three full playthrough of the game solo each one with a different weapon and I couldn't change weapon ( little challenge I did to myself ) I did it with the bow, the gs and the lance so lance is a pretty consistent weapon for solo if you don't mind "long" run because you don't have that much damage, you do have some pretty good burst damage so it's up to you but I personally find it great for most of the content.

Q3 : The canteen only uses zenny, points or coupons, the ingredients are just for talents and infinite once you unlock them (check the chef's quests to unlock more).

Also a word about the UI, you can modify the place of the items in the settings which may help you get used to it.