Yes, (1) is a short form of (2). The subject I and the auxiliary verb will are both understood to be elided. (Otherwise it wouldn't be grammatical: a future tense needs will and sentences need subjects.)
"I will be seeing you next week" is almost the same; however, there is slightly greater feeling of certainty. Your doctor might say that if you have a follow-up appointment in one week's time to emphasize that, or that same person could just use "see you next week".
By contrast, it would be somewhat unusual to say "I will be seeing you next week" to coworkers on Friday evening, whereas "see you next week" is fine. The reason is that we don't have a specific appointment to meet coworkers next week; it just happens because we show up for work. It's simply too many words to use for something that is passively expected to occur.
tl-dr: With perfect aspect, current/ongoing state is ambiguous. In your sentence, the time phrase may condition our view of the ongoing state.
I would interpret your original sentence as follows: at the point of retirement, you may or may not own one car, but you won’t concurrently own all three (in that case, you would have used ‘will possess’.)
Perfect aspect does not say anything about the current/ongoing state – that is the domain of the continuous aspect. Thus current/ongoing state is ambiguous, although we may infer something about it from the situation or other factors. For example,
I have owned a car.
It’s not clear if you currently own one, but we can infer that you don’t, because otherwise you would have just used the present simple. This is an inference, because the current state is ambiguous.
Different time phrases used along with perfect aspect may define (or imply) whether the action is ongoing or not. For example,
I have owned this car since 2011.
Clearly you still own it.
I have owned this car up to/until now.
Clearly you don't own it anymore.
It seems that with your original sentence, it’s the time phrase that conditions our view of the state of possession at the point of retirement.
Addendum: Concerning your idea about stative vs active verbs, I’m not sure if that’s relevant here. Look at the following examples.
By the time he retired, Alan had been married three times.
By the time he retired, Alan had gotten married three times.
Being married is a state, getting married is an action. But in neither case do we know if Alan is currently married.
Best Answer
Alternatively, if the project won't have been finished by this time next week, and you will continue to work on it, you say: By this time next week, I will have been working on this project for twenty days.