[Elecraft] K3 Purchase and Accessories Questions

[pastormg2 at verizon.net]

I am just finalizing what I might need on a new K3.  They have an option called the KUSB which I assume in a USB Port for upgrading the firmware.  I already have a  USB to Serial Port adapter that I have used on my TS-480S.  Would the KUSB be necessary?

Also I am not much of a CW operator but do operate PSK31.  I see an option for either a 5 pole 500 HZ filter or a 8 pole 400HZ filter.  Which would work well with this particular mode.  I also like to operate the other digital modes also.

And, I am more of a SSB operator as of the past few years.  I see that the K3 has standard a 2.7 HZ filter which I assume is 8 Pole but then again I'm not sure.  But there is also an option for a 8 pole 2.8 HZ filter.  Which would work the best for this mode?

Finally I will need to hook up my Amp. which is an Alpha 8410.  I'm not sure exactly what the cable is that I am using currently on my TS-480s,  But has anyone connected a K3 with an Alpha 8410.  And if so where did you purchase your connection cable?

I appreciate any advice I will recieve.  Mark KB3Z