Re: default route redistributed in EBGP
You are correct, Fortigate will redistribute all routes of a kind you tell him to + routes learned dynamically from other BGP peers. I.e. if you enable redistribute static - it will redistribute ALL static routes configured on it, unless of course you set route-map either in redistribute static clause or on BGP peer in outgoing direction. So if you have default route as static, enabling static routes redistribute will advertise it as well, unless filtered out with a route-map/prefix list.
That is all the beauty of BGP - full control over learning/advertising process, in OSPF e.g. you can't filter anything from learning, only control installing routes in the RIB.