need to add custom validation to checkout and customer form fields in magento 2

BILLING ADDRESS FORM AT CHECKOUT (user logged in OR out) FIRST NAME (LETTERS ONLY, REQUIRED) LAST NAME (LETTERS ONLY, REQUIRED) HOUSE NAME (LETTERS ONLY, NOT REQUIRED) HOUSE NUMBER (NUMBER ONLY, NOT REQUIRED STREET NAME (LETTERS ONLY, REQUIRED) CITY (LETTERS ONLY, REQUIRED) COUNTY (LETTERS ONLY, NOT REQUIRED) POSTCODE (LETTERS AND NUMBERS, UK FORMAT. REQUIRED) COUNTRY (LETTERS ONLY, NOT REQUIRED, DEFAULT UK) PHONE NUMBER (NUMBERS ONLY, REQUIRED)   SHIPPING ADDRESS FORM AT CHECKOUT (user logged in OR out) FIRST NAME (LETTERS ONLY, REQUIRED) LAST NAME (LETTERS ONLY, REQUIRED) HOUSE NAME (LETTERS ONLY, NOT REQUIRED) HOUSE NUMBER (NUMBER ONLY, NOT REQUIRED STREET NAME (LETTERS ONLY, REQUIRED) CITY (LETTERS ONLY, REQUIRED) COUNTY (LETTERS ONLY, NOT REQUIRED) POSTCODE (LETTERS AND NUMBERS, UK FORMAT. REQUIRED) COUNTRY (LETTERS ONLY, NOT REQUIRED, DEFAULT UK) PHONE NUMBER (NUMBERS ONLY, REQUIRED)   USER PROFILE AREA FIRST NAME (LETTERS ONLY, REQUIRED) LAST NAME (LETTERS ONLY, REQUIRED) HOUSE NAME (LETTERS ONLY, NOT REQUIRED) HOUSE NUMBER (NUMBER ONLY, NOT REQUIRED STREET NAME (LETTERS ONLY, REQUIRED) CITY (LETTERS ONLY, REQUIRED) COUNTY (LETTERS ONLY, NOT REQUIRED) POSTCODE (LETTERS AND NUMBERS, UK FORMAT. REQUIRED) COUNTRY (LETTERS ONLY, NOT REQUIRED, DEFAULT UK) PHONE NUMBER (NUMBERS ONLY, REQUIRED)