Could an earth-like planet form without accessible traces of iron
Without iron, you'd need a completely different biochemistry, and would in practice condemn the newcomers to a slow death. Iron is essential for hemoglobin synthesis and humans need to acquire it from food: from vegetables (most green leaves) or already concentrated in muscle tissue (by animals that still need to graze on iron-yielding vegetables). Similar considerations hold for copper, zinc, manganese, selenium and other trace metals.
Now the problem is that when you do have enough iron in the biosphere, iron oxyhydroxides begin to precipitate - all it takes is the appropriate environment (not at all uncommon) and voila, you get bog iron and can begin smelting. You would need some mechanism to prevent this; possibly some bacteria that sequester iron in metallorganic compounds that can not be refined without a lot of metal-based technology. Then most iron would find its way there, and you would need to harvest the bacteria to survive; at the same time, you could do with way less iron in the environment, and for both reasons there would not be iron(III) available to precipitate freely - and what little did, would be again eaten back by the bacteria.
Nutrients trade would be quite the enterprise on your planet - without careful husbandry of bacterial beds, people would suffer from all sorts of malnutrition syndromes.
(Now that I come to think of it, the bacteria might have been gengineered by the original colonists just to allow the planet to be settled, by concentrating/processing the required nutrients).
Let's do this
We start with a mostly silicate-carbon, metal-poor planet orbiting around a Population II (or the hypothetical Population III) star. It is uninhabitable due to unavailability of all except the lightest metals, but it sits smack in the middle of the Goldilocks zone of a suitable star, so terraforming is economically sound.
This is designed to become an agricultural/pastoral world. It exports, if anything, elaborated CHON. Technology will be well-nigh impossible (and this might actually be a desirable trait: whoever said, e.g., that the colonists were volunteers?)
What little dense elements the planet had (iron and nickel, essentially, together with any heavy metals from the Population III dust) has sunk towards the core, and is not practically reachable, but there's a nice asteroid belt not too far out. Ice comets are launched at the planet, while asteroids - they, too, metal-poor - are ground down to pebbles and dust, and the latter electromagnetically separated - in space, you can build the equivalent of an enormous mass spectrometer; particles with relatively high content of desirable elements are condensed again (sinterized?) and launched towards the planet. This goes on for a long time (self-replicating Von Neumann robots might come handy - of course they'd have to balance the need for metals and heavy elements to build themselves).
All the projectiles burn in the atmosphere, and water vapour and metallic ashes start floating down (metallogenic hits would be targeted towards the center of the continents to avoid losing metals to the seas). After many years, the surface is covered with a thin layer of metallic oxides, that rains force to seep downwards.
At that point the planet is "seeded" with algae, cyanobacteria and very basic (and sturdy) life-forms, that begin the transformation of the soil and the oxygenation of the atmosphere.
Other years pass by, and plants are seeded on the planet. These are much more aggressive and efficient in recycling the topsoil.
Water and mineral meteors will still be sent into the atmosphere: carbon dioxide, water and ammonia from the Oort cloud equivalent of this world will supply all the CHON we might ever want.
We start needing to sequestrate hydrogen; one (risky in the long-term) possibility is to stabilize it to methane (carbon is abundant thanks to carbonaceous chondrite meteors) and store in in undersea methane clathrate beds. Natural oil is another possibility, using biological Fischer-Tropsch processes to form oil reservoirs.
Several organisms are seeded, tailored to ensure a uniform spread in topsoil elements. Similar to worms, they would break down possibly dangerous concentrations of elements while aerating the soil (and there goes our bog iron).
Finally, there is oxygen enough to sustain Earth fauna, which is seeded from frozen ova by artificial robot wombs.
The whole "planet factory" could have been sent on a straight, high-acceleration trajectory towards the target planet, while a colonization ship follows. Such a scheme is presented in Robert J. Sawyer's Golden Fleece: the colonization ship spends the first four years, subjective time, going round and round the Solar System, accelerating to the speed of light. Then it sets off for a forty light-years travel to Colchis. There it will decelerate for another four years subjective time. The fifty years of the interstellar leg of the journey only take a few subjective days due to relativistic time-dilation, and the travelers will have experienced only a eight-year voyage, which is doable without suspended animation or complex generation ships.
Except that the whole scheme is a hoax. Colchis, at the beginning, is a uninhabitable planet whose probe images have been faked. The ship computer alters the flight plan so that the ship spends some additional subjective weeks, corresponding to thirty thousand years, whizzing around the Solar System at a much higher speed than officially planned. In this time, AI probes will land on Colchis and terraform it to match the fake images.
