Sounds like you need a good night's sleep xxx I know I had a few ups and downs thinking about another hamster. We have two now - a Syrian and a Robo - it isn't any more work than one really, as long as you have a cage. Although you could have 3 at the same time. Newt (Syrian) comes out about every 3rd night for 20 mins or so. Nugget (Robo) is almost impossible to get out but happy in his cage. I feed them at the same time so it's easy - a quarter of a slice of cucumber each or whatever and water and ham food topped up.
A baby hamster needs a bit more attention at first - they're so fast. Newt is now 7 months (I can't believe it!) and quite laid back. For the first few weeks he was clamouring to come out each night and I had a playpen set up and he'd just run around in there and on the spare wheel.
Taming two could be extra work, although it maybe would be at a later date.
I would suggest - however much you want a breeder ham - that waiting would be an idea. Get the little guy you fell for in the pet shop. When your old little guy passes on then put your name down for a breeder hamster. If the one in the pet shop has gone then that lessens the decision but adds to the frustration!
We can't predict everything - hamsters aren't always available at the right time and we don't know how long they will live, so maybe just try and relax - otherwise you get analysis paralysis!
I think pen and paper can help with these things. Write it down or write a list - how it would work with 2 or 3 - you get ideas when writing things down and it helps to see what's feasible and workable.
Could be a bit crazy with two baby hams and a little old guy and a full-time job. And a stressed you wouldn't be good for the hamsters either.
I have fallen for hamsters online for adoption, thought about it and then it's too late - then searched for more, not found anything, then found something and the ad is out of date.
You have four options basically.
1) Email breeder and ask if you can wait for one of her litters in the future and get the petshop hamster.
2) Get the petshop hamster and the breeder hamster and accept you may have three at the same time.
3) Do nothing for a week. Then it will be decided for you
Pet shop hamster will most likely have gone and too late to pull out with the breeder.
I sometimes think doing nothing is the best option if you're stuck. Either that or being spontaneous and that helps make the other decisions.
At the back of it all you're probably feeling a bit emotional about the stage your little old guy is at - it's hard seeing them age and decline and wondering what will happen and when. Very hard. So maybe that is what's making it hard to decide. It's why I didn't get another one before Charlie died. Although I wish I had in hindsight because it felt much more of a loss when there was no hamster to look after as well as losing a loved pet. So I would get another hamster now. Whichever one you get.
When you're trying to decide between two very different things there is no comparison really and it becomes an impossible choice so then it's almost toss a coin, be spontaneous or do nothing xxx