I have no idea what a good CTR would be for the fields you mentioned
You should start the campaigns, split test different ads with different images, headlines, CTAs etc for your remarketing campaigns and keep improving your CTRs
Is in your opinion the Remarketing a good solution, in terms of increaseing the PPC budget by a reasonable profit margin for these 4 market fields (a, b, c, d )?
if the website is set up correctly, then remarketing can work well for all of these. if it's leather bags and they added the bag to the checkout but didn't proceed, then you can target these people specifically and lure them back to the website to finish the transaction.
I assume with automotive the objective is to get their contact details in which case remarketing will work well
Which kind of PPC (other than AdWords) would you use for them?
well i don't know the specifics of the business so it's difficult to say
for online printing, if it involves printing photos, then fb marketing can work well. leather bags could also work well on fb
beds and mattresses -- you could try yahoo & bing advertising as you would probably get lower cost/click than u would on adwords