I've been playing MM1 for the past few days and having a great time with it, but currently my party has a scroll in their inventory to eventually turn in to someone in Dusk. I haven't rushed to Dusk because I've been exploring the areas in and around Sorpigal and Erliquin, but I am beginning to wonder if I should go ahead and turn in the scroll since it could be preventing me from getting any other quests? If I already have a quest filling up the party's single quest slot, would I even know that another quest is available so that I could decide which quest I want to keep and pursue? I know MM1 doesn't have hundreds of quests like some of the more modern games, but I can't help wondering if I'll never know about the few that exist if I happen to already have a quest.

Hopefully, my question makes sense, but being limited to only one quest isn't something I'm used to, so trying to figure out how it works.

No, you're ok. You can have as many quests as you like.

The "one quest only" refers only to Lords' quests. Basically there are Lords (you'll recognize them when you see them) who will give you a series of quests, and you can have a quest only from one Lord at a time. So if you get a quest from Lord A, you can't get a quest from Lord B, unless you finish that one first (or cast Remove Quest). But don't worry, that will come later in the game.

Other than that there is no limit to the number of quests you have.

Like most CRPGs of its time the quest system is rather primitive, and it's all handled by items, with the "quest flag" being "item in inventory or not".

ZFR is correct, you don't have to worry about lugging that scroll around. And if you do run into that situation with the Lords quests, you'll know, because one of them will say "you are already quested!" when you try to get a quest from him.

I forgot to mention that all quests can be repeated too. So if you ever lose that scroll or something, you can just go back and get it again.

That is especially handy! I can't remember all the times I've accidentally sold or used quest items that I didn't realize were quest items at the time. :)

Those delivery quests are a great source of money and xp early in the game I've found. Kitted out in the best money can buy and level seven really just sets you up to start what passes for the main story quest line.