Seam filler and base coat choices

[Ichibanpainting]

Don't worry about it the Tamiya primer won't kill the details at all.

As for filler yes any fillers you will be using will require you to apply it then sand it then most probably re aply it again and re sand it. On the Titan I'm working on right now I have to do those steps about 4 times on one leg just to make sure it was seamless. It's a long process but if your looking for a perfectly looking model you really can't skip this step. Some times I spend 2 or 4 hours just smoothing and sanding a model. The more you spend on prep time the better looking the model will be with paint on it.

[me_in_japan]

I have to agree - prep time is time well spent. For a regular infantry size mini 3-4 hours isn't unreasonable. For a Titan? Heck, I've been prepping mine on and off for years (ok granted I did completely take it apart a few times, but...)