Greetings Mr Newbie, allow me to introduce myself: I am Mr Veteran
I will answer your questions.
1) Yes it is open world like the fallout series
2) "Collectables" is open up to some discussion, but otherwise yes, you can aquire unique items in the game such as quest related items and unique armor and weapons
3) You can acquire many homes for you character in game, most if not all of the cities will provide you with some housing, but you will need to look around for the person who will sell the properties to you, these homes will have various price tags attached to them, and also vary in size and facilities, you can buy additions for your homes from people specified by the person who sells the house to you. You can also aquire player housing for free (ingame) by either purchasing or downloading Oblivion downloadble content online, most player homes availible from downloadble content have unique facilities to cater a specific type of character (thief, vampire, knight, wizard, ect)
As for families, no, the game's protagonist (main character) appears to have no blood relatives, as the game's storyline states that your character can not remember anything, this IMPLIES he has no family.
Friendships? again up for discussion, any kind of action towards a character whether it be physical or social can result in having various consequences, anything you do will influence people's opinions on your character. AI allies on the other hand generally come with factions and they will die for you so long as you have a high status with a faction. You can also summon creatures through conjuration, but you will have no social relationship with your summoned creatures.
4) Melee, Long Range and Magic are simplified catagories, yes you can master all these or even just one or can use one catagory in conjuction with the others.
Melee can be divided into the following sub-catagories: hand-to-hand, blunt and blade
Long Range is simply derived from the Marksman skill
Magic can be used either in conjuction with other catagories of combat or simply as a stand alone catagory; it consists of the following skills: Conjuration, Destruction, Restoration, Mysticism, Illusion and Alteration.
Magic is unique as you don't need to have mastered skills to cast advanced spells, loot acquired from enemies and chests contain scrolls which can be used to cast various spells.
Other skills which influence all three catagories of combat are:
Block, Heavy Armor and Light Armor
5) You can join multiple factions in a game, including but not limited to: Dark Brotherhood, Arena and Mages Guild.
6) Good question, 'been playing a lot of fallout recently and forgot about this one. There's a variable in the game called disposition and it affects how charcters respond to you, disposition is influenced by many factors on your character such as, whether you are a vampire or not, and whether you are allied with certain factions.
Disposition can be influenced by crime, and disposition will also influence how easy it is to "barter" (or in other words to get things cheaper) from shops, an easy way to increase disposition is to interact with a character by attempting to speak to them then switching to something called the "persuasion minigame".