That sounds like a good idea 90802, whatever works for you!
The main reason I like to outline my site before I start is because sometimes a site can look good from every aspect but then you find out that you really don't have enough Tier 3s to put under those Tier 2s (at least not relevant ones).
As for your question, I don't like making Tier 2s without Tier 3s underneath it because Tier 3s are made to bring traffic from low supply keywords AND strengthen your Tier 2. This is why I strive for at least 10 Tier 3s under every Tier 2.
Why does each Tier 3 strengthen a Tier 2? Because each Tier 3 links back to it's home (Tier 2) and therefore gives it more link strength. So I highly recommend that you try and have 10-20 Tier 3s under your Tier 2
About the amount of pages, I wouldn't worry about that. Some like to grow large websites and some like to do several, I prefer both but it takes a lot of time so it is understandable to not do it, you could outsource the content after awhile when your website is making enough money.
Good luck!