NORN KJOKL

1 en
2 tver
3 trir
4 fyre
5 fimm
6 seks
7 sjø
8 åtta
9 nie
10 tie
11 ellive
12 tolv
...
20 tuttu (Ork.)

No. 20 is only found iside Ork. Norn, therefore I would suggest *tjugu or *tjuo as the Nynorn "standard" (how much I hate this word), based on Far. tjúgu, Nor. tjue and Swed. tjugo.

Also, when counting, the neutral forms of 1, 2 and 3 are found, for example, in Far. and Ice. too, so that ett, tvø and tru should be used in the very same way.

Concerning tens 30 ~ 90, I suggest:
30 *triati
40 *før(u)ti
50 *fim(m)ti
60 *seksti
70 *sjøt(t)i
80 *ått(at)i
90 *nieti

as well as *hundrað (100), *tusund (1000) and so on.

To form the other numbers, we shouldn't stick to the main scandinavian (mainly danish-imposed) to write units in front of tens, then moving on the "purer" and easier opposite way, with or without the separator og:
21 *tjugu en
32 *triati tver
43 *føruti trir
54 *fimmti fyre
65 *seksti fimm
76 *sjøtti seks
87 *åttati sjø
98 *nieti åtta
and so on...

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en so mykid j Hiatlande ad segs skillingar ok XL hrentadi leigan a huerium tolf manadum... ok þar til oll ol gogn sidan fyrir vttan kannur ok diska ok potta ok onnur elld gogn er hon mintisk ei huorsu morg voru (Húsavíkarbrøvini, 1403)

These numerals are already done and you'll see them when the next 3 lessons are finally placed on the webpage. More or less it's the same as your guesses, one big difference is that there should be 'og' between tens and ones.
I preferred to use 'tuttu' for 20 because it originates from Old Norse 'tuttugu' and because words from Orkney or Shetland have priority over words from Faroes or Norway.