I am trying to restore my blog exactly as it was: content (text and pics), categories/tags, plugins, structure, Tarski theme with CSS and other options (changed header, various Tarski plugins, sidebar, alternate CSS).

(0 - I made a backup of the blog just in case. :-)
1 - I exported the content of my blog (>Tools>Export).
2 - New host, new database, new domain name, new installation of latest version of WP.
3 - I imported the content of my blog with the "Include attachments" option (>Tools>Import). At this point, content is on the blog, but the theme is the default theme.
4 - I thought uploading the theme and plugins files would restore the installed plugins and theme display. However, plugins are available but disabled. Theme isn't activated either.

Does anyone know how I can also restore the original Tarski theme with the exact display and options? Thanks.

The theme config is stored in the database. Same with the installed plugins. Tarski’s options are stored in the wp_options table; you can dump it out via a query like this:

SELECT option_value FROM wp_options WHERE option_name = 'tarski_options';

You can then reimport the serialised options value like this:

INSERT INTO wp_options (option_name, option_value) VALUES ('tarski_options', ' ...serialised value goes here... ');