Rose,
I am in a similar situation as you. I don't understand a lot of the stuff people are posting in this thread. I think I understand a lot of it conceptually, but putting it into action is another story.
Most people see the total portfolio as one big pie chart with all investment accounts combined, and decide on how they want to break up the pie into pieces (funds) depending upon what they are aiming for (agressive, conservative, tax deferred, etc). This, to me, is too difficult and confusing to do, because I have an old 401K's I cannot add any money to. I also have a current 401K I am putting a lot of money into every 2 weeks while Roth IRA (tax free) gets fed only once a year by a fraction of the amount of money that goes into my current 401K. You also have multiple retirement accounts like myself. And I believe that is why people are asking for more information so they can figure out the whole pie.
Besides that it is very confusing and difficult for me to try to figure out what funds to get to make one big pie chart (some accounts have few funds to choose from), if I made one pie chart with all my retirement accounts, and split it into different funds, some funds will get new money while some never will, and you did mention something similar in your post.
So what I decided to do was to look at each retirement account as a separate pie chart, and use similar asset allocation breakdown for each retirement account. If one asset allocation pie chart with all accounts combined is like one universe, mine is like having multiple universes, but each universe has same or similar asset allocations (depending upon what funds are available) as the other universes.
To determine asset allocations, I am using my version of Lazy Portfolio by combining some of the stuff I read in books and this link
Lazy Portfolios - Bogleheads
My current 401K moved to another brokerage firm with limited selections recently;, so I am going over the funds to figure out how I can match my current 401K to the asset allocations I want.
Overall, Anmorph post is very close to what I am doing. (2 and 3) except he is not mentioning to create multiple universes like I am doing.
I think his approach and my approach would make things easier to handle.