Amiga 2000 PAL to NTSC

[Zac67]

1) NTSC vs PAL doesn't matter for the PSU. But a PAL Amiga is bound to have a 220 V PSU.
2) You're probably using RGB, RGBI is 4-bit digital as with CGA. RGB PAL and NTSC are compatible, so that won't be a problem. Vertical sync / size may be a problem but is usually adjustable.
3) If the Agnus on the board is a universal type you can just close J102 (or fit a switch) to make the system boot up in NTSC. For genlock or advanced video compatibility swapping the clock oscillator will be necessary.
4) yes. Most monitors will work in NTSC mode and some also in PAL.

[Zac67]

However if u end up with an old A2000 that can't switch, then u all u hafta do is buy the "Fat Agnus" chip for it and plug it in and then u can switch video modes as u like.

... unless it's an A-model (German) A2000 with DIL Agnus. You'd need to replace it with an NTSC Agnus.