1 - The printer you have chosen is your max budget. It is a nice looking machine, but if you don't want to spend everything you have check out this link: http://www.3ders.org/pricecompare/3dprinters/
you can sort by country, price, lead time, and a lot more.

1A - Here is a better chart: http://www.productchart.com/3d_printers/

2 - I have not used ABS (no heat bed). As far as I know (and don't quote me) there's no issues with skin irritation, though I it is possible someone out there might have a reation.

3 - You shouldn't need to build a powerful desktop if your designs are moderately simple. If you were to model a car and run simulatuions in Solidworks, then yes you would need more power.

4 - 3D printers are awesome, and have used them over the last few months for personal and R&D work in the shop. The ability to see a prototype take shape, see errors as it builds, and save money (over first production run models) has been incredible.

5 - Yes. There are multiple printers that offer dual extruders. Check the link above. There are after market extruders that have 3 and 4 nozzels. Also, new product on kickstarter allows for up to 4 colors (or types) of filamint to be extruded to the printer, here is the link: https://www.kickstarter.com/projects...ref=nav_search

Hope this helps.