Upgrading what?

I would personally work from the middle in either direction, nearly always purchasing the best component you can manage. The exception I would make is the preamp. If possible, skip the preamp until the last piece is in place, but prior to getting carried away with cabling (that is if you do get carried away). Prior to cabling I would also purchase a really good rack like the Mapleshade Samson. If you can justify it, buy the rack before anything else. This way you will have a good reference point when auditioning equipment purchases.

Only after these things are covered would I recommend "voicing" your system with cabling or power cords. The rack and any isolation solutions should be in place before this "voicing" is commenced. I have personally found greater impact from power cords and speaker cables. Others have had a different experience.

If you are set on the speakers, I would ask the speaker manufacturer for his amp recommendation for that particular model. If you purchase an amp prior to your speaker purchase, make sure it is compatible with the speaker you expect to purchase in the end as well as being sufficient for the interim.

Set your sights high and try to make only one purchase per component. Patience is a virtue they say.

BTW, I agree with me too. ;-)

After looking at the threads you have already posed, I think you're ready to just pull the trigger. As long as your amp can drive your speakers, it doesn't matter so much in what order you throw your darts. Good luck

One factor not mentioned yet is the projected length of time you think it will take to build this system. If it is going to be a long time, then I would definitely move the speaker purchase up in the time-table. If it takes you three or four years or more, then you will be missing a great deal of the music by not having good speakers.
I agree with many above. Every piece is important and can result in improved sound. However, some upgrades will impact the sound more than others. I would say that speakers, source and then preamps are generally the most important links in the chain. With your good sounding source, I would jump the the other end, and work back from your speakers

I don't think there's a wrong way. First I would find out exactly what sound I am looking for. This can only be achieved from listening to different equipment. I don't care how good your front end is supposed to be. You can't make a Paradigm sound like a Martin Logan or a Magnepan sound like a Green Mountain Audio.It just doesn't work that way.Speakers make the largest impact in sound IME.Yes it can be changed or refined by a different front end to a degree. But not enough to fool someone into thinking you have a different pair of speakers.

Enjoy the Ride it is the Best Part!