database design - designing and planning a module -

i @ planning stage of creating new module magento. first magento project, while don't want complicated, try , stick best practices, leads me question.

the module creating newsletter facility various options user can edit. project meet following criteria:

• allow user sign newsletter
• to sign not have member of site
• allows various preferences automatically set
• allows set preferences edited user
• recognises country user in on sign up

my first thought create module without taking account of existing modules , add 2 tables store user details , preferences. have decided won't best idea , assume better utilise newsletter module?

would using raw sql acceptable add preference options? doing have to:

• add couple of columns users table link preferences , user
• add column identify if there member or newsletter subscriber
• add table user preferences

this leads me question if bad practice play core tables (i assume is)?

my main question is:

• what can research/leverage in magento complete first project, without becoming complicated?

as adding columns won't affect functionality. functionality affected when there alteration of tables.

i think best practice here 1) add specifics columns 2) override newaction newsletter module 3) change phtml accordingly 4) model functions

hope works fine