Help me decide

[Decoy68]

Hey all this is my first post and was hoping to find out information on whether a FR-S or BRZ is right for me. A little about myself im a 22 yr old recent college grad looking for a new car. i currently have a v6 chrysler 300 so one of these would be a drastic change. originally i wanted to get a dodge charger or challenger with a hemi. i have definitely always been a muscle car guy bc of the size and design of american cars. i saw the scion commercial and was intrigued bc i can get a brand new one and they look good for the price. now for the questions.

Are there any major differences between the FR-S and BRZ besides the minor cosmetic differences and the packages they offer?
Are aftermarket parts cross compatible and priced the same? i know there isnt many out yet but what have ya seen.
I am also a bigger guy 5'10 230. would i be comfortable in one of these cars?

Any other helpful info would be much appreciated. thanks ahead of time for any help and responses.