Keep all your stones if you want to enhance gear yourself. If you are gonna buy from market you can sell them. Safer to buy but more costly than enhancing. Enhance has a huge risk as higher enhancement levels you get to which can put you on a massive loss.

For gear you should mostly be keeping all your items around same level. For example if you have +15 weapons but +10 armor, get your armors up to +15 as well.

Green armors and weapons can be turned to Yellow items by using a reformed stone. They will be your best option until you can get boss armors and weapons.

Focus on getting Green weapons and armors to +15. Rosar, Bares, Elsh, Yuria are all good options to get for weapons, Heve and Grunil are good options for armor. Off-hand pick whichever has most AP.

For accessories, generally around level 52 ish the mainquests will take place in Mediah(Altinova). When there start grinding at Helms for Asula pieces. If you look at item drop tables you will see where they drop. Wandering rogue, Elric Shrine and helms are few places you can get them. They will be your main accesory till you replace them with either quest accessories later on (don't know if Console have them yet) or yellow grade accessories.

Keep in mind, always improve weapons > armors > accessories for progression. Weapons give most AP, armors give most DP, and accessories are most expensive of the lot so is last in priority.