A3000 hardware

[Amiga4k]

Is this A3000 an 68030 x 16 or 68030 x 25. Some older 2.04 units were shipped with 16 Mhz. You never stated this. An older 68030 x 16 is more limited in upgrade (not suited for 3.5 or 3.9).
Alas, you withheld your location area, so I am unable to offer parts without that information.

[Amiga4k]

There have been many great suggestions. Before you jump into an expensive upgrade, you must verify some chips. You absolutely must have a Buster 11, Ramsey 7, and DMAC 04 for an 040 or 060 card.
While your inside, verify the processor speed. Also you should check the SCSI (WD33C93A) controller chip revision. An 08 is preferred.

[Amiga4k]

Some 040's work with the older chip set, some do not. The 3640 rev3.1 and 3.2 need the newer chip set. The Apollo 060 (a problematic card, in m y opinion) requires the new chip set.  I have heard that Cyberstorm 060's require the Buster 11, as a minimum.
The 040's run hotter than on 060's.