CruelSummerLord said:
1) Is it bad DMing to out-and-out refuse certain character concepts or classes? I freely admit to being an old-school grognard despite my young age, and I intensely dislike the trend towards all kinds of prestige classes, multiclassing, min/maxing, and magic supermarkets.
One thing in here that trips my "The DM might not understand the game" warning system is the dislike of multiclassing.
I mean, let's face it: multiclassing has been in ever since the concept of race-as-class was divorced. (And, some would argue, was present before that: if you wanted a Fighter-Mage, you took Elf, etc.)
There is nothing inherently wrong with multiclassing. The system is specifically built to encourage it (and later iterations of the d20 system have encouraged it even more).
The reason for this is that a Fighter / Rogue is not necessarily a soldier who gives up his commission to go steal from people for a bit (and, generally, I've always hated that hold-over from the 2E dual-classing system). Rather, he's usually something more like a Spec. Forces operative, or a swashbuckler focusing on light weapons and armor and derring-do, or a Thieves' Guild Enforcer, etc. A Barbarian / Bard is a skald, inspiring others with his disregard for his own life. A Fighter / Cleric is a temple guardsman. Etc.
In other words, these characters aren't so much "multiclassing" as taking levels in the "My character idea" class.
A DM who straight-out disallowed multiclassing (or allowed it with "in-game repercussions") would definitely get the cocked eyebrow from me, and while it wouldn't necessarily stop me from playing in his game, it would cause me to stop and wonder a bit.
The other issue I see looming on the horizon is that if you're going to be running an extremely low-magic and low-gear campaign*, you are actually boosting the power of the spellcasting classes relative to their mundane counterparts. It's something to watch out for.
* - Depending on how you handle the "permanent and non-permanent goodies," of course.
Anyway, just some friendly advice.