Upload & Sell: Off
Is your monitor calibrated and profiled ? If not, then allocate some money for a Spyder 4 or an i1 display pro.
Changing from PC to Mac is not a trivial exercise - a lot of things work differently, or need alternative software that is not always fully compatible. Some have no Mac version or no Mac equivalent. Don't do it without careful consideration to the time and effort involved.
Be aware that the iMac has little or no expansion capability - you can't just pop in a new standard drive whenever you feel like it. And next time you upgrade you have to pay for a new screen too. Still, that's not much worse than upgrading a laptop.
If you are after an excellent monitor for photo-editing then the iMac is not it. Look for NEC, Eizo, etc. for excellent colour and tonal uniformity. Make sure the combination of viewing distance and monitor pixels per inch suits your eyesight so that fine details look good instead of having obvious aliasing.
Overall, you can be happy with any computer if the screen, mouse, keyboard and software is ok - even if it is slower than the latest and greatest. Don't waste money if you don't need to or can't get a benefit that you'll appreciate. For me an excellent monitor outweighs a speedier computer.