Today went MUCH better! 5 wees in the potty today and apart from a small dribble in bed after he woke up - no accidents! We even moved on to wearing pants or pj bottoms this afternoon, and his cousin came round for a play date and he stayed dry. I've been asking him every 30mins or so if he needs a wee or if he wants to try, but I'm not pushing him or making him sit down. Sometimes he says 'try' and then he tries and we don't get anything, but mostly he says no and waits. It's about every 2.5 hrs he says yes and has a proper wee. He is very excited to get to flush the toilet!
To be honest I've been a bit naive and didnt do any real research first! I've looked at the 3 day training and a lot of the elements I'm actually doing, though one version I read requires the lo to be naked from the waist down for 3mths afterwards which seems a bit extreme!
I'm certainly not expecting him to be dry at the end of the week, but if he can be dry at home then that's a massive step towards being fully potty trained. Also he's not even 2 yet, so there isn't that pressure either. I know from friends with older children it can be a bit competitive, and some mums have felt a sense of failure for not having them dry at 2.5yrs / 3yrs. If it doesn't work this week, then we try again later. No big deal. That said I do have in the back of my mind, that potty training when a new baby is about to arrive / has just arrived is a nightmare. Regression is likely, and trying to concentrate my attention on F while juggling a newborn would be difficult. It certainly would be easier if he is ready to be dry before the autumn.
One other benefit to potty training is the house arrest

We have done a lot of reading, puzzles and his vocab cards - quality Mummy time. I'm also planning on making scones and decorating plant pots for Mother's Day gifts with him this week.
Hands - I think it sounds like Dex could do it. I bet as his speech increases he'll be able to tell you and will be trained very quickly. He definitely sounds like a do-er. I'm always amazed how far ahead physically he is, in comparison to F. Especially when F's pretty capable as it is!