No problems. Most longboards are more or less those dimensions anyway, they are pretty standard. In terms of variation:
- anywhere between 8ft4 and 9ft4 will be ok - 9ft (+/- 2 inches) is ideal, but a bit shorter is ok. A bit longer is ok as well, but it starts getting unwieldy and you dont need it for your weight
- I wouldnt go below 2 5/8 inches if you can help it, but thicker is ok. Over 3inches might be a bit too much but doesnt really matter.
- for width, 22 inches is about normal but down to 21 (but no narrower) or up to 23 (or even a touch wider or so will be fine. Wider is usually better than narrower for a beginner
the only other thing to look out for is that you dont buy a 'gun' by mistake. A gun is specifically designed for very big waves, but is often 9ft or so long and so sometimes seems like a longboard (mal). The difference is easy to spot - a gun has a narrow pointy tail and nose; a mal / longboard has a rounded nose and more rounded tail
Gun

- gun.jpg (7.55 KiB) Viewed 756 times
Mal/longboard

- mal.jpg (73.12 KiB) Viewed 756 times