Hi, (1) And they toured constantly, from their origins in 1965 until Garcia’s in death in 1995. During this three-decade span, the Grateful Dead played 2,314 shows. During that time, Garcia became the most recorded guitarist in history.
Should it be Garcia's death? Please check. Yes.
(2) When his family moved to Menlo Park, 25 miles from San Francisco, Garcia started listening to KWBR, a rhythm and blues station, and developed a love of music.
Should it be for? Please advise.Both 'of' and 'for' are OK.
(3) This intense interest led him to delving into country music and joining up on with a friend, John “Marmaduke” Dawson, a country singer working at a coffeehouse in Menlo Park.
Should it be delve? Please clarify. It's OK as written, but 'delve/join' are better.
(4) But there’s no denying the fertility of the current scene. There seems to be no apparent thread, at least speaking in terms of genres, that binds these bands together. Perhaps, then, it is the enthusiasm of the scene’s fans, their passion for live music, that is its common denominator.
Should it be threat? Please advise.No. The idea of a thread here is something common that runs through both bands. We often speak of 'a common thread'.
(5) He remembers being awestruck the first time he heard Presley’s “Heartbreak Hotel.” While listening, he’d try to play along to the songs he heard broadcasting from the radio.
Should it be broadcasted? It's not wrong, but 'broadcasted' is also OK. Or you could say 'broadcast'.
(6) Soon after that gig, Gilmour met a music manager that wanted him to go to Marbella, Spain to play the tourist crowd there.
Should it be who? Please clarify. Yes.
(7) While he’s demonstrated an ability to shred, or play very loud and fast, he’d better known for his precise and passionate note choices.
Should this he'd be? It seems to need 'He's'.
(8) He two moved into an abandoned house and jammed daily, and with the aide of a couple local musicians, they hammered out some covers, including Iron Maiden’s “Remember Tomorrow,” and they played some nearby parties.
Should this be couple of ? Yes.
(9) Metallica toured that summer. In Boston, Massachusetts, while on tour with Anthrax, the truck with the band’s equipment is stolen---the only gear left are the guitars that John Marshall stashed in his hotel room, concerned that the extreme cold outside would warp their necks.
Does the bolded phrase form a complete thought in this sentence? Define what you mean by 'a complete thought'. 
It's an adjectival phrase describing 'John'.
(10) That fall, they returned to Copenhagen to record Master of Puppets with Rassmussen. Released in the beginning of 1986, the disc has a 72-week run on the album charts, and becomes the band’s first gold record.
Should it be had? You can say 'has/becomes' or 'had/became'. The use of the 'Present in the Past ' makes the reader felel more like 'he is there'.
(11) The 100-plus members of the symphony were directed by composer/arranger Michael Kamen, who’s history with Metallica dates back to 1991 when he orchestrated “Nothing Else Matters” for the band’s self-titled album. As the main songwriter of the band, Hetfield’s rhythm playing does more to effect the overall sound of the band than Hammett’s who’s lead playing has to adhere to the structure of Hetfield’s chord progressions and song structure.
Should it be whose? Yes in both cases.
Clive