Upgrading HD and/or adding in SSD

Why did you push the RAM to the max here? What are you doing that requires this much RAM? If you need that much RAM then the internal storage I/O your system has may not suit your needs. This is where a Mac Pro maybe a better fit for you. Now moving to your HD SSD question - Your system has a PCIe interface for an Apple SSD blade. I would recommend doing that first Vs swapping out your HD. As to swapping your HD out for a SSD - Yes, you can do it but... you have a 3.5" HD and now a 2.5" SSD so you'll need to buy an adapter to house the SSD (not all adapter frames will work here). To be honest your giving up large storage space HD for a smaller space higher speed SSD. If you do a swap out. I don't think thats what you'll want, as then you will need to have some external HD connection via Thunderbolt. I would go with the dual drive setup HD with SSD for the best setup if you stay with the iMac. But your best move is the Mac Pro (new) for what you want here.

Thanks for your answer. So, I understand that it's better to don't swape out the hdd, with the ssd, cause it's too small respect the internal Hdd. I really would like to have a dual drive with Ssd within the Hdd, but the procedure it's too complicated for me, and the Ssd that I bought it's not the right device. How can I go on to put a fusion drive in my iMac?

If is it possible, can you link me the right procedure and guide?

Thanks Dane

Yes, the sizes of the devices are different (would need an adapter frame to make it work). And Yes, its better to use the Apple SSD PCIe connection to add in a second device (SSD) within this iMac (to create a fusion drive if that is what you want). This is the IFIXIT guide to follow: SSD replacement. It's a lot of work and I would classify it as an advance project (not a 1st timer job). As you have maxed out your system RAM wise I have a feeling this system is not powerful enough for you which is why I pointed you to the new Mac Pro as a better direction. A low end unit has the level of expansion options you are looking for and a lot easier to work with. Review these IFIXIT guides Mac Pro note the difference! Given the risks of damaging your iMac trying to expand it with an SSD it would be cheaper getting a new system which you can work on (expand still again) in the future.

Reference this repairability gage on your iMac IFIXIT Guides vs the Mac Pro above 5/10 vs 8/10

I saw the guide for replacement SSD, yes it's a work for professionist.

I appreciate your advice about Mac Pro, but right now I can't bay it.

I would like to have the fusion drive, I, didn't put in the order cause the crazy prices of apple. About the Crucial SSD that I bought, is it possible to extract the Ssd on its case, and put it in the right place with Pcle connection? If will be possible, I'll give this job to a professionist!

If it's not possible, I'll consider to replace the hard drive with a 2 Tb hard Drive of 3,5 " maybe, but I really prefer using the fusion drive, cause I put on my MacBook Pro early 2011 and it works quite good. Tell me how to procede,

Thanks a lot!