Sincere motivations? What??? Are we talking about the same man who assassinated countless of his own partymen, including some of his most talented comrades like Strasser in the night of the long knives? There's nothing sincere in that just psychopathic powermania. Same as e.g. Stalin.
Sincere motivations such that he was doing his best to actualize his ideological plan. Essentially he was logically trying to get towards a specific goal and taking any action that furthered it, and said goal does not involve the destruction of Britain. This does not mean his goals were by any means kosher to the average modern person, but if he was actually trying to do them everything he does makes logical sense.
Killing English people -> less Germanic people
Conquer USSR -> more living space for Germanic people
Etc.
Now i say again, if you think that his political actions cast doubt on the sincerity of his ideological motivations then we might as well stop discussing it. I dont have sources at my access to convince you (unless you are willing to take my word on my university education), so we might as well stop discussing it. Debating my opinion vs yours with no solid third party sources is pointless, yes? Im convinced based on my schooling and personal research that Hitler had real goals and wasnt just a madman, you seem to have the opposite idea. These cannot be reconciled and neither of us has information to prove our position.
Edit:
I should add paranoia doesnt in validate ideological motivations. In fact id argue in this case it supports it since Hitler thought his party members were incompetent and wouldnt be able to execute his plan. Thus, removing powerful party members is a good idea to reduce the risk of an internal coup.