how to begin plugin-development

hi there!

i already read throug beginner guides for plugin development so i know a few basics.
now i would like to do it a little more professional.
so first thing before i start is to ask people who already know things.

what i want:
– maintainable code
– separate user-interface from logic
– don’t change the theme (want be able to install updates without losing my changes)

so in my plugin i’ll have several entities, for example countries, towns, persons and homes.
some of them i could manage with custom-post-types(countries, towns, persons) and fill them with meta-data.
others i think i can’t manage with custom post types (homes) there i think i would need to create a custom table and add the fields i need to store.

so when i have these i would create the views for the front-end.
one that lists all countries and let’s me filter them and the same for towns and persons.
one for a country where i would like to see all information about the country as well as a list off all the towns in the country.
similar views for towns and persons as well.

now the question is: how would i create these views. i would like to separate it from the logic by using a template engine like smarty or twig.

can you provide me with an example of a plugin that works like this?