Congratulations on your new family member!
To answer your questions:
1 Applaws is a really good dry food. They also do a (supplementary) wet food. Cosma is similar. It actually looks almost edible to humans, so he may like that? I mix a little water into it for my cats. Just to ensure they're getting plenty of water. Ensure he has fresh water all the time.
2 No crap in nearly 3 days? If nothing by tomorrow, I would definitely ring vets. He's not crapping elsewhere is he?
3 Presumably you have him booked in for registration and general check-up with his new vet? They can either sell you some Stronghold, which does fleas and worms (possibly not tapeworms though), or write you out a prescription, which you can use to buy it online somewhat cheaper. Advocate (fleas) and Milbemax are also good. Again, these are only available from the vet/prescription.
I use Advantage for fleas and Drontal for worms, bought online. But I know my cats' weight etc.
Any medication type stuff bought off the shelf is generally rubbish, and often dangerous. You're right about the Frontline, it's become ineffective.
Photo of your lovely languorous long-haired cat please! 