It's always good to start with a plan and explore the available options.
Some questions, because you have some contradictory statements in your post:
First you say you want to 'sync' with items in separate tables.
Then you say,
Product A is a record stored in the "PV Modules" table. This record, of course, contains fields, such as an image that is specific to the record/product. When I select product A from the drop down menu (which I know how to do already), I would like the image container box to update with the image container field used in Product A's record.
That's 2 different scenarios. Do you have a master record (from which table/relationship?) on your layout, where you want to pick a different record from the dropdown, and go to that record with all the pertinent information
Do you just want the dropdown to select an item, and add it to the main record (like an invoice with a portal to line items)?
The first type scenario would be more of a master/detail module. The second scenario is more of adding a picker list. In this second scenario, you would use calculations or lookups, like you would in an standard invoicing solution where the dropdown selection triggers a script which depending on how you have your layout set up and which table/TO's are connected), adds what you selected to the main record on they layout, usually in a portal.
Both of these are easily googled on all the FM sites & blogs with many examples
Is the panel on the left (with the dropdown) a portal or a popover?
The second option, apologies for not being clear. Fields on the kit builder interface should draw information from other tables, but add it to the "kits" table (separate).