What's the goal? Pure science and survey or true colonization?
Technically and operationally, it would be Mercury and the Belt, but you need a strategic goal/purpose for the political backing...
After that, island-hop to the outer planets.
If there's a research base on Mars and an orbital lab around Venus by 2000, Mercury is the obvious next step inwards and the Belt (Ceres or something else with a decent amount of useful rock and ice) outwards, figure by 2010-2020 using the man-objective-decade approach.
After that, Jovian System by 2030 and Saturn, Uranus, Neptune, and (possibly) Pluto-Charon by 2070. (2069 would be a resonant target date, if all is as historical up to Apollo XI).
Then, dig in and build up population and sustainable industries on the Moon and Mars, with as much survey work and resource exploitation as makes sense elsewhere.
Best,