Z Reddit Mentions | ChartExchange

Lately I've been thinking about how people usually have many investment objectives with different priorities, and not a single pass-or-fail goal as it is sometimes assumed for simplicity's sake (still better than the all-too-common pseudo-objectives of the 'make as much money as possible as safely as possible' sort, of course).
To make a simple example, a person could easily have the following four objectives, in decreasing priority order:
1. Have at all times access to at least $X for unexpected expenses;
2. By the age of 65 onwards, be able to withdraw from investments at least $Y/year ($Y being enough for a tolerably comfortable life, but not an especially luxurious one);
3. By the age of 55 onwards, be able to withdraw from investments at least $Z/year ($Z>$Y being enough for a fancier, earlier retirement);
4. Leave as much money as possible to successors, compatibly with previous objectives.
Of course it could get more complicated than that: for example, one could have a 'be able to withdraw at least $W/year while still working if I feel like it' objective or a 'gift $R to children before starting retirement' one sandwiched between objectives 3 and 4.
Now, I'm not sure if this is the best approach; but a simple way to deal with this could be to build a different portfolio for each objective, and start working on the lower-priority ones only when the higher-priority ones are already being adequately funded.
So for example Objective 1 obviously calls for an emergency fund - i.e., a very low-volatility 'portfolio' consisting of a MMF or something of that sort. Once that is funded, one might go ahead and start working on Objective 2, which calls for a standard stocks/bonds portfolio with the bond allocation steadily rising over time as you get closer to your goal; if after investing enough every month to be reasonably sure to reach it one has still money left they could start working on Objective 3, which probably calls for a more aggressive portfolio of the same sort; and so on.
I can see drawbacks in this approach - for example, it can be difficult to decide what 'funding adequately' means - but it also seems to me that if we have multiple objectives of this sort we *should* account for it somehow.
As a bonus, I think that looking at things this way makes it easier to understand why sometimes it makes sense to go "When you've won, stop playing" and other times it makes sense to go "When you've won, start playing harder": if you can reach an objective while taking less risk obviously you should do so, but if you have already effectively reached it perhaps you can also start considering some lower-priority objectives (which might call for a more aggressive allocation for their sub-portfolios).
Does this make sense? Thoughts?