Hi,
the only way WP-Table Reloaded interacts is with loading the tables from wp-Table's database tables, upon request for an import.
WP-Table Reloaded will not interfere with wp-Table or change anything from it, it only reads the data once and stores it in its custom data structure.
That (for your second question) means to store a two-dimensional array as a serialized string in the "wp_options" table. Thus, WP-Table Reloaded does not use its own database tables (like wp-Table does) but it uses readily available methods from WordPress.
All this means: You will not lose any data of the old wp-Table (nothing is overwritten), even when the same table ID is used. However, I do not encourage using both plugins at the same time. This is due to slight differences in the Shortcodes the plugins use (WP-Table Reloaded uses [table id=1 /], while wp-Table uses [TABLE 1].)
So, the recommended way is to go to the "Import" screen of WP-Table Reloaded and use the import feature at the bottom to load the tables of wp-Table. You can then use them in WP-Table Reloaded, and I would then encourage to change the old Shortcodes of wp-Table to the new ones of WP-Table Reloaded (likely with a changed table ID!). After that, you should remove wp-Table.
Best wishes,
Tobias