GER can build a "modest" navy and do surprisingly well with it, as long as they operate within range of land-based aircraft. If you venture too far out, the RN carriers will make life miserable for your fleet, unless you develop and build your own CTF and CAGs.
I've used those two old WWI "battlewagons" to tie up the RN long enough to perform a landing on the UK coast, without building a single ship other than a group of 3 transports. Once you've got an airfield and a port, the UK is pathetically easy to take out of the game: I've done it in one game as Italy and even once with Hungary with only 3 TPs for the actual invasion and a sub as a spotter (although in that instance GER joined the invasion around the time I already had London and 2/3 of the British Isles under control). Taking out the British Isles with Germany is so simple in HOI3 that I avoid it (as an obvious exploit) until after I've crippled the RN to the point where it can't even muster a ship to threaten the landing.
Yes, veterans of the system can take advantage of AI weaknesses to smack the bejezus out of it. I've conducted landings on mainland JAP with just NATCHI's single starting transport before ;p.
But the OP is saying he's not even familiar with large scale troop deployment or, really, the naval aspect in general (not just by personal admission, but he also built a full run of both DD and CL). So I didn't want to give advice on how best to exploit poor AI (poorly/undefended UK isles, for example), I just wanted to give him the heads-up on what will happen when he does what he said he was planning to