After buying the Ultimate Edition, i found some more stuff, you would think you get everything included with the Ultimate Edition but i guess not.
Forza Horizon 3 Expansion Pass $34.99 (Not included in Ultimate), but if you own Ultimate, you will get a discount of $10.
Forza Horizon 3 Horn Unlock Accelerator $2.99 (Not included in Ultimate).
Forza Horizon 3 Treasure Map $2.99 (Not included in Ultimate).
I got what it said on the tin. Always read the tin 
ie the Ultimate Edition description tells you what it includes.
EDIT: just on this I don’t want those extras so would not want to pay extra for them ie I would not want to pay more for the Ultimate Edition just so that it includes horns…
I am happy with the knowledge that I will get 6 car packs. Anything else I would prefer to make a separate decision on.