Right, long post coming...
First off, all kids are different. You need to potty train your child when they are capable of doing it, for their own health and dignity. That may be now or it may not be for a while as it depends on your child.
Your child sounds capable to me - age, good communication skills (told you when they'd peed), aware of pee (as demonstrated by them telling you), and has decent bladder control (held it for ages when no nappy to go in). That all sounds really promising!
However, if you've just brought the potty out of the blue with no previous discussion and it's freaked him out and he's resistant and upset - I say abandon ship ASAP for now.
I would recommend talking about the potty and toilet. Take him with you to the toilet and explain what it has happening. Tell him soon, when he's a bit bigger, he will use the potty and he won't have nappies anymore. Buy underwear and show him them. Read stories about the potty, watch TV show episodes about it. Obviously not loads, just thread some references to it throughout the next few weeks. So it's familiar and he knows it's something that is coming.
Then in a few weeks, try again - stay home for a few days, try the bare bum/loosely Oh Crap method for the 4 days you have at home. If you've made NO progress in that time, I'd be super surprised, but fine, park it again for a bit. If you have made some progress - even if it's just a bit - send him to nursery with loads of spare clothes (ideally commando if they'll allow that, our nursery does) and commit and just continue.
I will end by saying I'm absolutely not a potty training expert, this is just based on a lot of reading I've done, and training my own kids - DD at 26 months (pretty easy and basically trained herself, unicorn potty trainer!), DS at 33 months (trickier but still fine. We are two weeks in now, commando, has the odd accident here and there, and still not fully comfortable with pooping and so is withholding a bit). I think DS would probably have been able to do it a few months ago but I had ill health for months until recently so it had to wait. Hes been dry overnight most nights for the past week too which has been a shock, as DD is 6 and still in nappies overnight! They are all different.
Oh Crap is a decent book but I never followed it as a bible, and the Eric website is great. You could also speak to your health visitor for guidance.