Power Supply k1823 and K7203 Transformer and Fuse and enhancements

Hi, does anyone can help me to understand how Velleman suggests the transformer for the K1823 and K7203 power supply kits?

K1823 - LM317 based 0-30VDC @ 1A max

1 - Suggestion is 24VAC / 50VA or 28VAC / 50VA - with this one I can understand, I just can’t get a 28VAC, can I use a 30VAC? I did some calculations and it’s supposed to have at least 28V DC with a 24VAC…

2 - Fuse suggested, is 250mA at mains (before transformer)… If we are consuming 1A, why 250mA?

K7203 - 0-30V @ 0-3A

2 - again fuse here is 800mA, is it enough?

And now… what about add a voltmeter and ammeter to K1823 and K7203?
And… having the possibility to vary current, limit current, is it possible?

Thank you in advance.
Alex.