I think the Boss katana amps have a recording output on them so you could use that straight into your audio interface instead of micing up the amp.

Adding effects post recording gives more flexibility to make changes at a later date than recording with the effects in place.

What DAW are you going to be using? There's a lot of tutorials on YouTube for the most popular DAW's out there, I use Reaper myself and if I've ever been stuck YouTube has always had the answer so far.

If you plan to do a lot of guitar based recording it may be worth you looking into guitar cabinet Impulse Responses too as they can be very useful in getting the right guitar tone in a mix.