If you load your existing save, all your perks are reset and your cyberware technically isn't installed properly until you visit a ripperdoc (Vic will call you with a quest to visit). You get 1 free attribute reset also. Any removed items will be flat out gone from your inventory. All the legendary/uniques will be legendary tier5 by default if you're max level. If you horded upgrade components, it is fairly cheap to convert them to legendary ones. You can upgrade any t5 legendary to t5+, which usually buffs it. Be careful though, some "upgrades" actually nerf some stats in exchange for others and some of the upgrades are hardly worth it. They also got rid of some of the attribute requirements. Like Panam's sniper rifle doesn't have that body requirement to fully use now, for example. Some weapons or cyberware do scale bonuses with certain attributes, though.
They changed a shitload, so if you haven't played in a long time it will feel pretty newish in how the game plays