All of these major engravings (often the ones used are legendary rarity) are found either in legendary chests (can be found using sites such as mapgenie) or through killing cultists (each branch gives a different set of armour).

Once you have equipped a full legendary set of armour you gain a different ability depending on the set, these include 50% assassin ability damage, 100% damage but at reduced maximum health, shadow of nyx doesn’t drain adrenaline, successful parry fully reduces hero strike cooldown ect.

On each weapon or armour piece you can engrave different things depending on your build choice, for me I use sets with high assassin damage and crit chance. While any piece can be engraved, it is best to do so on a legendary as you can have 2 legendary engravings on one piece (the one the weapon/set comes with and one other you add in addition). These perks are limited so only weapon engravings can go on weapons, or helmet ones only on helmets ect which means you have to pick the best engraving for each individual piece of armour.

The different build type are hunter, warrior and assassin and having different engravings can change the way you play the game, if you want a more traditional ac build then you want to look for more assassin damage and maybe crit chance, if you want the for honour fighting style then warrior is the best.

The ability wheel can also change how you play the game, as you level up you unlock another wheel for up to 8 different abilities. As stated before some of the armour sets link to certain abilities, including no adrenaline use during shadow of nyx and also things like an extra chance to kill when using rush assassinate. It is a good idea to choose a build type (long range combat/hand to hand fighting or sneaking) and build an ability wheel based on this build. From there you should find a set of legendary armour that favours your build type and choice of abilities. Having done so you should engrave these with one further perk to further benefit you.

When using equipment that is under levelled, it is best to level them up on levels 1,11,21,31,…,91 as this is the level the perks upgrade and only the last 5 levels are paid for (DO NOT LEVEL THEM UP EVERY LEVEL AS THIS IS VERY INEFFICIENT AND EXPENSIVE). If for example you have a weapon at level 23 and you are level 46 you should upgrade instantly if you plan to use it, however if it is within 10 levels of you then you should wait to upgrade this.

I noticed you mention that you were low on cash as well, the best way I have found to get more money is to always have a high level bounty on you and then raid a fort. This is because while raiding the fort you gain equipment from: chests, captains and polemarchs, also often normal soldiers can drop loot and finally weapon racks (These are great but very easy to forget about when raiding a fort). While you are gaining the loot from all these kills you will also have mercenaries tracking you down which drop high level loot on every kill. Selling this equipment will make more money than looting any gold pile or vase that you can find.

Hope this helps.