But.... If I am not mistaken, the D5000 supports metering with old AI lenses while I seem to recall that the D90 does not.
Is that correct?
No. Good God. This isn't that hard. The D200, D300, D700, D3, Fuji S5 Pro etc. have everything, they can meter with old manual lenses. They can also autofocus with AF and AF-D lenses as well as the AF-I and AF-S lenses with internal motors.
The D100, D70, D50, D80, D90, Fuji S2, S3 have a motor and so can autofocus with Af, AF-D, AF-I and AF-S lenses. They cannot meter with non-electronic lenses like MF AI and AI-S ones.
The D40, D60, D5000 have no in-body motor and so can only focus with AF-S and AF-I lenses, they will not meter with manual focus lenses (barring the odd AF-P or chipped nikkors).
If the OP doesn't know what this means then I'll wager the D5000 will do a fine job.