The "ch" is as in loch, not as in church.
"Fawr" is more like vow-r, with the ow as in out, and the r pronounced. It means great or big, so literally perhaps "great thanks", or indeed "thanks a lot".
F and ff are pronounced as in of and off, and there is no v. Welsh is almost entirely phonetic (you write what you say) -- it's just that the sound values are rather different to those of English, and there are some extra sounds.