I have had great success using a machine polisher, this link will take you to the Dual Action version I use. http://www.cleanyourcar.co.uk/polishing-machines/das-6-pro-dual-action-polisher/cat_81.html (you will need to make 240v AC 850W available)
I would avoid anything that looks like an angle grinder, in the wrong hands you can get swirls and worst case burn through the paint.
Be careful to select the right polishing products, "avoid silicone based products" appears to be a common recommendation if you need to do any paint repairs in the future. Personally I avoid T-Cut.
For what it's worth I use Meguairs #105 and #205, a UV sealant Menzerna Power Protect and Chemical Guys Wet Butter Wax but please get advice from your painter or someone else in the know before you start work.
P.S. I have no association with cleanyourcar except being a satisfied customer.