I actually got the strategy guide today.
Weapons are stacked, but it looks like there's more than one missile. You're not restricted to just one type and then the upgrade. Or at least that's what I gather.
Information about the Characters and Hunters:
Spoiler : click to show/hide
Samus Aran
Little is known about the origins of the bounty hunter Samus Aran. She is believed to have been raised by the mysterious Chozo race after her family was killed during a space pirate raid. When Samus reached adulthood, the Chozo created the Varia Suit, giving her special cybernetic abilities. Soon after receiving the suit, Samus began working for the Galactic Federation, her first Mission taking her to the Metroid-infested planet of Zebes. Samus continues her service to the Federation on a freelance basis.
First Admiral Dane
Fleet Admiral Castor Dane is known for his utmost dedication to protecting the Federation from its enemies. He is stern and aggressive, and has a strong dislike for Space Pirates. Rumor has it they orphaned him at an early age, an act he still seeks to revenge.
Rundas
Rundas is capable of generating and manipulating ice. This trait is common among inhabitants of the moon Phrygis, but Rundas is one of the few who have used this ability for bounty hunting. Subject is known for getting results, but considers himself without peer. His arrogant demeanor has led him to mainly seek solo missions, and he rarely works with others.
Ghor
Ghor is a cybernetic bounty hunter, capable of merging his body into larger mechanisms. The most common of these is his armorsuit which doubles as a gunship and provides him with a formidable combat arsenal. The merges are often accompanied by a shift in personality, replacing his normally calm demeanor with an aggressive attitude. He demonstrates a high proficiency with all things mechanical and is often called upon for missions requiring computer infiltration or manipulation.
Gandrayda
Gandrayda possesses the metamorphic ability to assume the form and abilities of other creatures. This talent has led many to seek her out for stealth and reconnaissance missions, despite her powerful combat abilities. Details on the subject's origins are unknown, but her unique traits have made her a sought-after hunter for missions.
Dark Samus
Target is composed of pure Phazon energy and is highly unstable. Scans indicate that Hypermode attacks are capable of disrupting her, likely a result of Hypermode being energized by Samus's body. Dark Samus is capable of generating "echoes" of herself to aid her in battle. These units are used as increased firepower and act as distractions while she replenishes her energy; they should be destroyed immediately. She is capable of absorbing energy from Phaaze to replenish her own (dunno what Phaaze is).
Also, there appears to be online content, but only in the sense of sending someone "Friend credits" which help unlock bonus material.
And no on-system multiplayer, either, seems like.