When starting out, the heroes get to purchase from the alchemist and market.

When a week starts, the first hero to go to the market only gets to turn over a number of treasure cards equal to the city's market rating (and may also purchase from the entire deck of shop cards).

Are the four heroes also so limited at start (such that out of the four heroes, they will be able to purchase at most the two random copper treasure cards that Tamalir has on a given week), or can they purchase out of the entire copper treasure deck (up to 1200 total gold)?

EDIT: In fact, it occurred to me that the rule may be intended to only permit the purchase of shop items, and no copper treasures at all. Is that the case?

Also, does the alchemist limit apply to potions for initial purchases (e.g. no more than 2)?

I'm pretty sure that at the START of the game, before "week one" starts, the heroes can buy only from the normal market deck. No treasures allowed. Then, DURING the game, if they want to shop more as a market action or a refitting, then they get access to [x = market value] treasures.

I think they can initially buy as many potions as they can afford. They are not "in the game" yet.

I don't think the heroes automatically get to visit the alchemist and market (the terminology is different on page 8, where starting is described). They get the standard game's full access to standard city store items and potions (without a cap). They don't get to look at copper items. If they want to visit the market to view copper items, they need to spend the first week in Tamalir or use a restock action after using a dungeon glyph.

We've always played that the heroes could buy unlimited potions and town shop items only, no treasures, before the start of a campaign.

I always "limit" the amount of potions to the number of counters I have. If we're out of counters, the shop/alchemist is out too!

Since the most number of potions the heroes can possess is 12 (3 per hero) how can you run out? I'll have to count up my counters....

Heroes can also put potions in their backpack, I remember a game in which the heroes turned most of their money into healing potions, they ran out rather quickly...

Also, if I did not misinterpret the latest FFG rules update, you can never buy treasures in the market until you have opened at least 1 chest of that type of tresure. This would mean that the heroes can not buy any treasures in the market at all until they have gone down a dungeon and found a chest.

Hmmm...I only thought that applied to Vanilla Descent. In fact one of the strategies for beginning the first dungeon is to glyph out and get copper equipment at the market. That way you're not stuck with beginner's equipment.

I'm afraid you are misinterpreting. The ruling you are referring to actually came up in the FAQ a long time ago, and applies to regular Descent. (It wouldn't make much sense in RtL anyway, since the whole concept of "campaign level" sets what you can purchase.)

To my knowledge, there's nothing that says you can't buy treasures right off the hop. You can buy as many copper treasures as you want with your 1200 starting gold. Which means four. However, the draws are picked randomly off the top of the deck, not hand-picked.

From my experience, buying all the necessary goods will leave you MAYBE with a couple potions if you're lucky. The heroes certainly don't have enough starting cash to afford treasures on top of that.

I think it works the other way around, there's nothing that allows buying copper treasures under those particular circumstances.
In vanilla Descent, you aren't allowed to purchase any kind of treasure until you've found at least one chest of the appropriate colour, in RtL the trigger to allow the heroes to buy a specific kind of treasure is to be in the proper phase of the game, since the first equipment phase happens (IIRC, though I have been known to have erred before) before the actual copper phase of the game starts, you're not yet allowed to purchase copper treasures, you have to wait for the first market week/first turn so that the market gets stocked with a few copper treasures...

I think it works the other way around, there's nothing that allows buying copper treasures under those particular circumstances.
In vanilla Descent, you aren't allowed to purchase any kind of treasure until you've found at least one chest of the appropriate colour, in RtL the trigger to allow the heroes to buy a specific kind of treasure is to be in the proper phase of the game, since the first equipment phase happens (IIRC, though I have been known to have erred before) before the actual copper phase of the game starts, you're not yet allowed to purchase copper treasures, you have to wait for the first market week/first turn so that the market gets stocked with a few copper treasures...