usability - big form VS steps/wizard

In a form to insert products/services (in wich products will have extra data for products that are composed by a mix of quantities of other product(s)) is it better to have a large form with all the fields there and showing the extra fields when "it's a composed product" is selected running the risk of a lot of fields being overwhelming for the user but having everything you need right in front of you and just fill it in. Or dividing this form in steps and follow a different route in case you choose 'Product' (to select if it's composed or not) and then again a different route if the Product is Select as a composed one.

My inclination is for the latest approach but then I think it might take a lot of steps.

what would happen when creating a Service:

Description and Reference->Is it a produtct or a service?->Brand->Service Family->Service Type->Stamp duty and VAT->Want to had a image?->Any extra observations?

when creating a composed product:

Description and Reference->Is it a produtct or a service?->Is it composed?->Add the products and quantities that compose it -> Brand->Product Family->Product Type->Stamp duty and VAT->Want to had a image?->Any extra observations?

EDIT

also my problem with giving feedback, in the steps/wizard approach, is the fact that there will be a different number of steps according to choices made during the process

EDIT2

Ok i've been trying to figure it out and think I might have a solution. If I aggregate a few actions in the same step is it a bad idea? (because the user performs up to 3 actions but the step is still the same)

Step 1: Description and Reference->

Step 2: Is it a produtct or a service?->Is it composed?->Add the products and quantities that compose it-> OR JUST Is it a produtct or a service?-> (in case of a service)

Step 3: Brand->

Step 4: Product Family->Product Type->

Step 5: Stamp duty and VAT->

Step 6: Want to had a image?->

Step 7: Any extra observations?

What are your thoughts on these?

Also Franchesca's latest suggestion is interesting but i don't really like the idea of changing the size of the steps along the way, it seems like it gives somewhat of an inconsistency feeling.