First off, you really want to finish a few things before you start your weathering. You should add your markings if you are going to, as those should be weathered just like the rest of the vehicle. Nothing looks more 'off' than clean bright markings on a dirty tank. If you are putting decals like stars and such, those should be put on next.

I would also consider your tools. If you are painting them you want to get that done as well, like metal for the tool heads and wood for the handles. (if you are planning to paint them) You should really paint the tires on the road wheels at this stage as well before weathering. Maybe even the .50 cal.

The whole 'seal the decals with future' thing is really up to you, it's something that I feel got posted on the internet and then spread like a virus. It isn't absolutely needed and not nearly as important as the web will have you believe. I've used it and I've also done entire models full of decals and never used it. The 'gloss surface for washes to flow' etc. is another really over exaggerated internet fallacy and in fact, can often times work against you with the weathering as it is just far to smooth and slippery. Sometimes youtube can be very helpful, other times it just serves to confuse us.

AK Interactive products actually perform better on a matte or satin finish as they have some tooth to them, gloss is too slippery. Because they are enamel, there is no need to seal the acrylic as they shouldn't have any effect on one another.

I would focus on finishing the detail painting of the items mentioned above before weathering, and at the very most, apply a satin varnish over the decals after complete.

HTH