When I first began using Odoo, I used the technical interface to create new fields in existing models.  So for example I added a text field called x_Reseller_ID to the res.partners so I could store State Reseller Identification #'s. 

Now I am a little further along in my progress of understanding module development and have begun adding fields by installing addons.

My question is, what are the advantages and disadvantages of using both methods?  

For example, if I have 40 custom fields, if I made 40 addon's will this have an effect on performance (obviously in the real world I could consolidate fields into 1 addon) vs just adding the 40 fields to the existing models by adding them in the technical interface?

What happens when I update?  I expect I could lose my custom edited views, but can I lose data in my models?  

Reason I ask is I still have several fields with data in them that were created using technical interface.  I am wondering if I should go through the trouble of making modules for the same data and then migrating the data from x_Field to Module_field or if my data is safe.