I am also tandem feeding my two boys (29 months and 8 months). As Feeb said the biggest heads up I can give you is that you may find he drops feeds as your supply decreases. I really noticed my supply drop at around 25ish weeks. In fact I'm sure I had very little to no milk left, but the good news is DS1 kept feeding I also found I had nipple sensitivity, which I think peaked at around 12-16 weeks and then settled right down again.

I have found tandem feeding to be a lot easier than I imagined. It was tricky with a newborn (who had a few health issues and was in SCN for about a week) and I actually stopped feeding DS1 for about a week while I was in hospital and recovering from some nipple damage. Again, he went back to the breast no worries and now I'm starting to hope he weans soon-ish! LOL.

Good luck, wishing you all the best!