How to determine which harmonized standards are relevant to achieve CE conformity declaration
The first thing is to figure out which EU directives that apply. You seem to have gotten that part correct. 


LVD directive applies if supply is >=50VAC or >=75VDC. For productions containing radio, the RED directive states that LVD directive applies no matter supply.
EMC directive applies to all electronics, unless it contains radio. Then RED directive supersedes the EMC directive and covers EMC aspects too.
ROHS directive applies to all electronics. It needs to be considered during component choice and PCB assembly. 
WEEE directive applies to all electronics (with a few rare exceptions). It needs to be considered during product marking and aftermarket logistics, to ensure recycling. You probably shouldn't need to address this one in the EC declaration for the product, but on an organizational level.


Looking at any of these, you get a big list of harmonized standards from the "EU official journal". The best bet is to consult a test house regarding which ones that apply. Keep in mind that they love to charge money for lots of tests, so they will always suggest more standards than needed.

I'm not such an expert, but a qualified guess (these standards change all the time):


In LVD directive , the relevant standards are most likely the monstrous EN 60950-1 + friends, regarding electrical safety. Miscellaneous product-specific standards may apply. Maybe EN 60529 for IP class, ensuring that users can't accidentally stick their fingers inside the product to pet the 100VAC.
In EMC directive, it depends a bit on area of use requirements. Some flavour of EN 61000-6, immunity &amp; emissions. If the product is something humans will touch, either during use or during maintenance, then the ESD standard EN 61000-4-2.
In ROHS directive, EN 62321.