I would wait outside as long as you can - if dinner is burning or the phone is ringing, put your puppy in a crate or keep him on his leash and take him inside with you for 10-15 minutes and try again. If you CAN stay outside, stay out (walk around a bit, mine ALWAYS go if we walk, even just to the neighbors house and back) and wait. An empty dog is a GOOD dog

After just a few weeks of this hassle, you'll learn your dog's signals, schedule, etc. Trust your judgement and if you end up with accidents, then go back to what you were doing before
Don't soak the food overnight. Only let dry food be wet for less than 30 minutes and then throw it away. You don't want bacteria to form.
If you are worried about your puppy not eating, like if he isn't gaining weight, feed him a GOOD quality canned food. It's *extremely* important you only use a HIGH quality wet food, OK? Like:
Merrick
Nature's Variety
Innova
There are others, but you need to find a store that carries those brands and they will have many other good brands. You can't get this stuff at Petsmart, OK? You have to find a small store like a boutique or a feed store. They will have high quality dry foods too, which is good too (and more convenient) It's OK to feed wet food if you brush their teeth (high quality wet food is actually less processed than kibble, therefore better for them) but kibble is more convenient. Mine get both, mostly kibble, occasionally canned because they like it.
If your puppy is growing but just isn't interested in each meal, cut down to 3 or 2 meals. If you want him to eat on a schedule (you do, for potty training) then take the bowl up after 20 minutes. Once he misses a meal, trust me, he will eat the next one!!!
You are doing good with the potty training - it will feel like forever but in 6 months he will be on auto pilot and all of your hard work will pay off. Mine ring a bell to go outside - I no longer have to keep track of their schedule, they let me know when they need to go out. But I put a good 6+ months into training each of them, making sure they were empty, etc. before they got it
EDIT: LOL I just saw you are in Ireland - so those brands may mean nothing to you. So pick some canned food out and READ the ingredients, stay away from by-products and try to find a little shop with someone who knows their brands and can help you. Stay away from the pet supermarket type stores for food.