It usually takes about 50-100 years before you are no longer able to rely on Earth for all your mineral needs (depends on starting size and how aggressive you build up). Venus usually contains vast amounts of materials that won't run out for centuries even with thousands of mines. Civilian mining does help a lot of times (you just have to remember to actually pick up the material). For your first colonies, you would want to prioritize planets that are easy to colonize but have other bodies in system with large amounts of materials (so you can stick auto-mines and mass drivers on to send resources to the colony). However more benefits colonies have is luxury resource generation and tax revenue, so Mars and Luna (and other bodies similar in colonizing cost) are still good to grab even though they may not have resources (but as a secondary).
I do a few things for the fuel situation.
1) Fuel harvesters/dumps in forward systems with gas giants.
2) Efficient engines(0.3 to 0.5 on commercial, and 0.8 to 1.2 on military {except fighters and FACs}).
3) I usually put a Sorium Harvester on exploratory ships.