the 107 is much easier to assemble than the 109.
Also, there are virtually no instructions for the 107 - if I recall it was just an inventory list, and a picture of the model showing the resin parts in a different color.
Look closely at the pics on forgeworld and the normal riptide, that will help a lot.
If I recall -
Assemble the legs and torso.
Then you put the extra resin armor pieces on the legs, followed by the new big chest piece.
The arms are pretty striaghtforward (don't lose those little pieces) then figure out how you want them to look before gluing the shoulders to the weapons/body.
Here is a vid naming some of the parts...
https://www.youtube.com/watch?v=j4FgBmgY63Y
I made mine a lot more complicated as I magnetized him to be either a 107 or a "normal" riptide.
(unless you are exceptionally experienced in magnets, I would not suggest this).
If you have never worked with a resin model before, check out the section on the
fw site about working with them (advice on cleaning, glue, etc.).
Both are really cool models - I hope you enjoy them and your amry!
(I have not built my 109 yet, but he is on my 'build list' for later this year).