Legion's game design set up BFA to feel bad when weapons were made to be removed but player were not to retain their benefits in some way. BFA will set up the next expansion in the same way with the removal the azerite necklace leaving the next expansion in a similar place where classes will feel empty and no actual amount of character progression has occurred over the next two years.
There are addons for ElvUI on Curse, but unlike the other addons on this list, ElvUI itself can has to be downloaded separately. Despite this, it is probably the most useful in terms of UI customization. ElvUI is a complete UI overhaul that allows you to fix many of the basic customization issues that the original WoW UI has. The big drawback to ElvUI is that it is a bit of a time investment when you first download it. It takes a while to get used to, and you’ll have to take the time out to fully customize your UI. This can feel vastly different from other addons that are mostly set immediately once you’ve installed them. If you’re willing to put in that time though, this can be a really effective tool in organizing your menus, and having a better visual experience playing WoW. With this addon, you won’t need some of the other ones, such as Bagnon, which ElvUI already has built in.
FYI: If you’re returning to WoW after an extended absence prior to patch 5.0.1, it’s possible that you’ll have more than the maximum pet limit and/or more than 3 of a kind. However, this will be the only time that you’re allowed to surpass these limits. You will have to pare down your collection, eliminating your duplicates, in order to add new pets.

The most simple thing is TradeSkillMaster. This AddOn shows you quite an amount of information in the items tooltip. In my opinion, DBRegionMarketAvg the best source. It tells me the price, an item was posted on all EU realms in the last 14 days. Why not DBMarket? DBMarket only shows you the items value from your server in the last 14 days. This value often gets manipulated. Some people start to post an item with a 500g value for 500.000 Gold on the auction house for several weaks. As a consequence, DBMarket is rising towards 500.000 Gold.  If you use DBMarket with 100% and post your item for 500.000 Gold, nobody will buy it.