To be honest I'm not a fan of potty training birds and at this stage there's really no point. He's too young. You can easily remove the poop with wetwipes or special f10 wipes. Personally, I have the f10 wipes handy and every 20 minutes I watch for the bum wiggle and I can usually catch it. It's not like dog or cat poo, it doesn't smell so and it's easily cleaned up as they don't splat like normal bird poops or at least they shouldn't. The eggfood might make his poops more liquidy. If he's not drinking for himself then you need to keep up the fruits, veggies and eggfood. Birds don't tend to drink that much as they derive most of their fluids from their foods. If you do decide to go to pellets eventually you will need to ensure you feed plenty of moist foods like that however a varied diet is what I believe in but its really up to you how you want to proceed after weaning. At the moment you are doing great so don't change anything now. This will give you time to research and decide what you think is best. Personally I feed my birds on a mixture of seeds (no sunflowers except as a treat) and sometimes sprouted, pellets (TOPS), fresh fruits and veg, pulses (like beans) in a soaking mix, occassional eggfood when molting or as young birds and some treats like pellet berries (nutriberries but made of pellets) by Lafaebers. They also get cooked brown rice and sweet potatoe mash has been a particular favourite recently.
Its great you getting him on fruit and veggies ASAP. It's so much easier when they are younger. Keep up with the eggfood, if he starting to pick up seeds that's great but just keep feeding him until he starts refusing it. Although if he's refusing all foods you need to get to your avian vet. Leave a bowl of water in there for your bird he will figure it eventually

You should also monitor weight. I use kitchen scales and a bird carrier. I weigh the empty carrier, then the carrier with the bird in. Then subtract the weight of the carrier. It will give you at least an approximate reading until he's old enough to start training. Or if he will sit still on the kitchen scales that's great.