(Spoilers for the Travel East ambition, obviously)
The stat-boosting legacy items (Horizon Codex, Manual of Miracles, etc.) are always retained, even if you successfully reach the East. However, completing that ambition does remove any lodgings, heirlooms, scion, and money, and reduces all stats to 1 except Hearts (although the next captain will start with the usual 25 in each stat, plus any bonuses for stat boosters and possibly Hearts from the Shipmate legacy). So you do get to retain half of your Hearts, one officer, and the stat-boosting items (and of course any Trophies from completed ambitions in the lineage). Even though you lose heirlooms, lodgings, etc., it still might be worth getting them in case your captain suffers and untimely death before making it to the East. (Besides, a family in London is a great source of cheap Terror reduction)
If you plan on heading East then you might want to focus on boosting your Hearts as high as you can, since it’s the only stat you can pass on. You can do this by creating shrines to Stone and selling them at Adam’s Way, which gives +7 Hearts each time you create a shrine. You also might want to keep one of the upgraded officers (I recommend the Nacreous Survivor, since by an odd quirk of the Zee, your next captain can have both the Nacreous Survivor and the Nacreous Outcast. The Survivor also lets you increase Hearts to 150 without need for shrines to Stone. And no, unfortunately you cannot pass on the Keeper-Moth).
As for ‘cumulative’ effects in a lineage, I suppose you could consider the primary stats to ‘accumulate’ over time if you always select the same legacy. For example, if your first captain reaches 100 Iron (which requires +75 iron from the starting 25), dies, and passes Iron to the next captain, that one starts with 50. If that captain reaches 120 Iron (which now requires +70 iron from the starting 50) and passes on half of Iron again, the next Captain starts with 60 Iron…and so on. This really only works if you always select the same legac(ies) over and over. Since you can pass on two legacies at most, there’s no way to slowly maximize all stats for a new captain.
Your upgraded lodgings are also retained across a lineage, at least until a captain travels East.