so I want to create a character that is a Druid who rides on the back of a bear nearly all the time.... do you think I could flavor this or do you think I would need to add a few ranger (beast master) levels into the mix? In my head I’m picturing melee attacks coming from the bear .... but magic coming from the gnome ... if they are separated... the bear would not function ... I’m almost treating the bear like a weapon ... thoughts ? 

There's nothing stopping any character having a companion - the Beast Master Ranger allows additional benefits like increasing proficiencies for the beast and so on. Otherwise a beast companion is just the beast that follows your commands (most of the time). It would have it's own inititatives and attacks and on your turns you can cast spells. The beast would only be able to move on it's turn, though, so you wouldn't be able to do much with your own movement on your turns since it will take like half your movement to mount/dismount.

You would also have to keep in mind that a beast companion has no magical bond to you, it can disobey you and teaching it to do things it normally wouldn't like sneaking would require training and even normal interactions can require animal handling checks so I would recommend having proficiency in that. You'd need to discuss with your DM. However, there is nothing in the rules stopping you from having an animal companion regardless of what race/class you are.

Quote from Stormknight >>

I'm not sure what level of character you're thinking of, but if it's 3rd or higher, you could see if your DM would let you have the Find Steed and use it to summon the bear?