If you're on a budget, you can go with the ChainReactionCycle Brand-X Ascend dropper. If you're ready to put a little bit more money, you can get the Marzocchi Transfer post. This is the exact same post as the Fox Transfer Performance post but for a lot less money (Fox owns Marzocchi). This is the move I've done last fall.
https://www.bike-components.de/fr/Marzocchi/Transfer-Intern-Performance-Elite-125-mm-Sattelstuetze-Modell-2017-p61669/For the stem, Kalloy Uno 7 stems from Ebay are the best bang for $. And they are also light and strong. Something in the range of 50mm or 60mm.
My choice for handlebar is MTZoom. You can buy them at xcracer.com and I would get a 760mm unless you're really small.
For the seat, you clearly need to find one that your but likes. It's so personnal that it's hard to suggest anything. WTB Silverado and Volt are what works best for me but lots of people don't like them.
Tires are also personnal. Your location and riding style will dictate what you want. But for trail riding, you can look for those:
-Maxxis Chronicle (XC/Trail)
-Maxxis Ikon+ (XC/Trail)
-Maxxis Rekon+ (Trail/All mountain)
-Maxxis DHF Plus (All mountain/Down Hill)
-Maxxis DHR II Plus (All mountain/Down Hill)
-Schwalbe nobby nic (Trail/All mountain)
-Schwalbe Rocket Ron (XC/Trail)
Hope this help a bit.
Good luck!