Yes he was.
- The first hint was after Rachael's void comp test. She asked him if he'd ever taken the test himself.
- Deckard dreams of unicorns, which means nothing by itself, but when that other blade runner left an origami unicorn outside his flat, it meant he knew that he dreamt of unicorns. How could he know this? Because those dreams had been implanted in his brain like Rachael's childhood memories were implanted in hers.
- After the final fight with Roy, Roy saved Deckard's life because he had clocked him as a replicant. When Deckard is hanging off the building by one hand, Roy says something like, 'To live in fear, that is what it is to be a slave.' Deckard is at the time very frightened, implying that Deckard is a slave, i.e. a replicant.
- After Roy's death, the other bladerunner with the walking stick and the limp says something like, "It's a pity she won't live (about Rachael), but then again, who does?" The answer is Deckard lives, but only if he terminates Rachael.
I am broad agreement with your assesment, but with a couple of comments.
Re 2. Gaff is just a copper, not a blade runner, but he has access to Deckard's implanted memories, hence the origami unicorn.
Re 3. Both Ridley Scott and Rutger Hauer have a different interpretation for why
Roy saves Deckard.
Re 4. I understood this comment to mean that neither Rachel nor Deckard had much time left (inception dates).