Yeah, going from a 21 to a 28t is a huge difference. 39x28 is plenty of gearing IMO if you are young and relatively fit.

BTW, that is clearly a cassette, not a freewheel. Should be reasonably easy to swap some cogs.

RE the toe clips: yes, I saw that some pictures had them and some not. If they don't fit they don't fit. You could acquire longer clips, or space them as mentioned. However, IMHO, you won't get the full benefit of toe clips without the cycling shoes that used to go with them. Realistically, those are no longer available. Some 'touring' shoes would be helpful though. But, clipless is a more logical way to go. All the benefits of clips and straps and cleated shoes, but way more comfort and convenience, This bike is from the transitional period, so they won't look out of place.