The only place you need to configure the IP Helper command is on the SVI for the specific subnet that you want to provide DHCP services for.
From your scenario, I take it that you have the core switch and all the different subnets are created on the core. Vlan10, Vlan20 etc. The default gateway for each subnet would be created on the core. On each interface configuration you would add the IP Helper statement.
Assuming the core has trunk ports connecting all the remote switches to the core switch.
As long as you ensure that the trunk between switches will allow each Vlan, all you need to do on the access switch is put an interface in the correct Vlan.
On each access layer switch, you do not need to create a layer 3 interface for each subnet. You could, but I don't really see why. All you need is a single IP (usually the Loopback0) for management. Since the switches are all trunked to the core, the SVI that is setup on the core will handle the DHCP request and forward it where you want.
