Given I'm sure I'll change my mind about what features I'll eventually need, I won't be trying to finalise everything in the architecture plan. However I will need to figure out the major modules, how they all interact with each other, a sample interface standard, and at least figure out vaguely how they should all fit together in a sample game.
Then I'll need to start building the thing. Given I'll need to test the engine as I develop it, I'll also plan a series of minigames to try out each new feature. I'm thinking of starting with a resurrected "Project Nova", the scrolling space shoot 'em up game I was developing last year, since it will work with minimal game design work and art assets, and as such is easier to develop on a laptop. I'll probably be able to find a bit of time while I'm away to get some work done on this, provided I make a good development plan.
Regarding resource management, I think I've been overestimating how much work I need for that area. Given I'm aiming for a sort of retro feel for my next few games, hopefully this means I can get by without any fancy memory mangement schenanigans. Frankly I don't suspect my games will ever push the boundaries of the memory available, mostly because it'll take too long to actually create enough esources to fill them.
However, I wish I had the capability of testing the minimum specification for games. I'm assuming that most development houses have a series of different computer parts they can test their game's performance with, deriving the minimum spec through trial and error. But is there a way that you could emulate older computers, if I wanted to see how a game would run I had a Celeron processor?