Terry,

I would qualify my remarks by stating I have not built the Ches 18 specifically. In general terms though, I don't think it matters too much where you start. Some folks do all the fillets at once. Some do epoxy tack welds first then come back and do the fillets after checking that everything is stiil in alignment. I personally prefer the tack weld approach because it allows you to "set" the final shape of the hull before committing to fillets. It's easier to come back the next day and break a tack weld or two to repostion panels if something shifted. Then again, some folks do most of the fillets all in one setting, depends on your comfort level. Enjoy the process.

I always do the tack weld step.  Then I remove the wires so I have a clear path to make the fillets.  I also take the extra time to run a strip of blue painter's tape on both sides of each seam (aligned about with the stitch holes, so half an inch away from the seam).  This allows me to pipe in the fillets (plastic bag with corner cut, just like piping frosting) then smooth the fillets with an old rubber spatula, and then pull the tape which leaves a nice, clean, small fillet without a lot of messy clean up. 

My first build I then waited a day after filleting, sanded everything smooth, and then applied the interior fiberglass.  Second build I was bold and did the fillets and laid the cloth while they were still wet.  I wouldn't recommend this on your first build, but once you get the process down it makes for nice smooth seams with no sanding and does help keep the glass in place while you're squeegeeing (is that a word?). 

As I'm sure you've seen from the forums there are as many ways to do each step as there are people who do them, so read all you can and then decide what you're most comfortable with. 

Very helpful techniques.  One thing I am learning:  the first build is a lesson builder!

I've now done a build with tack welding and without tack welding.  Without a doubt, though it's a bit of extra work, the tack welding step is cleaner and much less epoxy was used in the fillets, plus all the wires came out afterwards.