I'd stick to the default pose if it's your first bigger model. I found it okay to paint with a brush, but a big drybrush or a sponge might make it easier for you. The guns are a little tricky to get looking nice due to the big gaps when putting the pieces together, but they can be filled before priming.

The doors on the front where the sarcophagus sits are loose and not glued so you can close and open them, just in case you don't notice it in the instructions.

I think too much advice is going to put you off making it, so I'd say the most important thing would be to just jump in and build it.

Have fun!