Problem is most planetary projects are going to involve time and/or unthinkable energy if done by physical means. The same amount of effort is more likely to get workable space in an orbital platform, and/or altering/engineering the humans to live on the planet as is.
Barring that, best move is probably to drop off some aggressive microbes to do your terraforming for you. After all, the Earth was methane-based until our oxygen-issuing bacteria showed up and slow murdered the previous biosphere in favor of ours. Something a little more engineered might speed things up.
At the extreme you could biobomb a world with something like the biome supremacy weapons of the Cthhorr.
https://en.wikipedia.org/wiki/The_War_Against_the_Chtorr
In any case of terraforming you will have to deal with whatever morality is involved in wholesale murdering the native life, which any terraforming of whatever technique is bound to do.
Also, any bioforming you introduce that is aggressive in nature will need to have an off switch so that any 'tools' that hitchhike offworld doesn't destroy your other worlds, and you can settle on it after the planet is 'ready' without side effects.
Finally, on the topic of seeding the planet you are going to need a complex balanced biome with the ability of the local flora and fauna to eat and fend off introduced species at whatever role/size, as will inevitably happen in an interstellar society.
Could be your first indication of another interstellar empire is running into planets they have already bioformed, no settlers or just outposts, seeding hundreds or thousands of years in advance, and you signal your boundaries by seeding yours. Overwriting the other seeded worlds may be cause for war, even though no individuals or fleets have met.
World Tamer's Handbook has a nice bit on what atmospheric gases would be retained per gravity level per world size. That's a good starting point for doing hard science atmo.
I don't know to what extent it would be functional to build up atmosphere only to have it bleed out. Starting up a magnetic core isn't casual either, and may not be possible on metal-poor planets. If you have the energy to manipulate on that scale, might as well build your optimal planet outright.