Should I CE marks the PCB if:
1.I sell the entire product as a kit?
2.I sell only the exclusive parts, making available instructions to mount them with other components (not sold by me)?
sell entire product
If you want to sell the entire product, you should satisfy all applicable directives, one of them being the EMC directive(1).
If product A is EMC and product B is EMC, then their sum is not by definition also EMC. So, you need to prove the entire product satisfies the EMC directies, having to perform all EMC tests again...
sell exclusive parts
If you sell exclusive parts, you might avoid the EMC directive (not sure about the other directives) refering to Article 2, clause 2 (d)
equipment the inherent nature of the physical characteristics of which is such that:
(i) it is incapable of generating or contributing to electromagnetic emissions which exceed a level allowing radio and telecommunication equipment and other equipment to operate as intended; and
(ii) it operates without unacceptable degradation in the presence of the electromagnetic disturbance normally consequent upon its intended use;
as the aluminium structure and the PCB will satisfy this exception (can't say it from the unknown 3D component)
or avoid the EMC directive by writing in the intended use of your product it is only for professionals to be used solely at research and development facilities for such purposes, and refer to Article 2, clause 2 (e)
custom built evaluation kits destined for professionals to be used solely at research and development facilities for such purposes.
The text at the end of Article 2
For the purposes of point (c) of the first subparagraph, kits of components to be assembled by radio amateurs and equipment made available on the market and modified by and for the use of radio amateurs are not regarded as equipment made available on the market.
applies to radio amateurs and cannot by definition be generalised to everyone.
(1) Another one is: Restriction of Hazardous Substances in Electrical and Electronic Equipment, and there are also General Product Safety, WEEE, etc)