The Nikumi is not a big boat at 19" wide. I have never paddled one but assuming you are also new to kayaking I wouldn't think that this is not a good choice. Now if you have paddled a lot and just new to building that's different.

I built a modified version of the Sea Ranger. It's 20" wide with hard chines and it's a tippy feeling boat. Not a boat a newbie is going to be comfortable in. I am not totally comfortable in that boat. Just putting a foam pad in the bottom to sit on raised the Center of Gravity to a point that the boat is very uncomfortable stability wise.

Recently I loaned the boat to a smaller paddler, Steve weights about 150 lbs vs my 200 lbs and he had no problem with it. I could tell immediately it was more stable with him in there than me. After a few minutes he was ripping around in it no problem. So your weight (and a lot of other things) have a big effect on how stable it is for you.

Assuming your are new to paddling, the Sea Tour design might be a better choice to start out in. Then again, if you can start and be comfortable in the Nikumi, you will be a better paddler faster than starting with a more stable boat.