Oh I've been wondering how you were but I didnt want to look like a stalker 
It's odd going to see them isn't it? I think it's a very individual choice but if I hadn't have gone, I think I'd always have regretted it. I also think it helps reduce the disbelief you feel at the whole process.
I wrote a letter and left it in his coffin.
May seem ridiculous to many but it helped me (as well as a load of pictures, photos, toys from his grandchildren who insisted he needed them to play with in Heaven) 
there was barely room left for him!
I'm glad (?) you are managing to rub along with your mum. I know how terribly you are hurting, but she's lost her practical focus too atm, so as you say, all the appointments/sorting/planning has just boom-gone.
She will struggle with that a bit, if she's snappy, please don't think it's you.
Grit your teeth, roll your eyes 
That's the times I miss mine, we'd be pulling faces behind her back conspiratorially.
Yes, the vessel in which your wonderful Dad travelled may have gone, but the thoughts, values, personality he gave you, as well as the memories are all still with you. No one can touch them.
Be gentle with yourself, you can get through the funeral, celebrate him.
Have you managed to agree on everything you wanted as content? If there is anything you want to say or do for the day, do it. Don't worry about what anyone thinks.
This is his send off. You will honestly feel strangely calmer after it. 