You get a crossbow.
You don't get the crossbow, the crossbow was taken totally out of the game after the initial trailers were already made.
There are 420 flags you will need to collect for Assassins Creed (good luck finding them all)
you have to collect all the flags in Roma. Once you do that you exit the Animus and you will told that Ezio went to Spain. This then unlocks extra memory sequences that take place in Spain.
Assasins Creed: Collect the Flags in each City/Zone. Kill the Templars. Assasins Creed 2: Improve the Villa Collect the Fethers Purchase all Armor, Paintings, and Upgrades. Complete the Codex Collection You can also kill guards, and civilians, but not horses. Oh and you can also kill yourself :)
Ezio is awarded the Borgia Cape. It allows you to do the same thing as with the Auditore Cape. You gain no Notoriety, but are still pursued for breaking the law.
If you find all of the 101 Borgia flags and 10 feathers that have been scattered around Rome in Assassins Creed: Brotherhood, then the diabolically stylish (and Notoriety-eliminating) Borgia Cape will be yours. In the first game, you just get all the related achievements.
Personally, i have the 1st Assassin's Creed and what you do is that there are side missions like retrieving flags or you can assassinate guards in the city's that you do your missions in. Some missions are pickpocketing people to get info on something. In another mission you have to kill the leader of this city.
Only if you wish to achieve 100% completion. It's not necessary if you're just playing the storyline. And no, you won't get anything out of getting them.
8.5-25 hours dependsyou plw you play it if you just rush through the game 8 hours if you explore get all the flags and such it could take you up to 30.
Yes, Desmond can jump back into the Animus and go to any area as often as you like to get any items you missed.
flags
Flags.
Collect and studies flags.