I'd second pretty much all of that advice. The basic mechanics are pretty simple and the only time I find myself having to stop and think is if NPCs are using powers where the mechanics are written from the players perspective and you have to reverse the
[attribute <- attribute] calculation and then get them to roll the dice.
For the first few sessions, keep it simple. Plenty of time to add in more detail if it morphs into a longer campaign. There's lots of great stuff in the Advanced Players Guide, but my group's been playing for several months and the only bits from the Alternative Rules section that I've used extensively are the Distance Categories for missile weapons and Encumbrance, which to be honest I enforced at the start, but now pay lip service to. My players don't try to take advantage and if they find a heavy or bulky item, we figure it out in the narrative. They've just discovered the possibilities of Alchemical Weapons, so that's going to be interesting.
If you haven't already, grab the Symbaroum Reference Sheets pdf from The Iron Pact -
http://theironpact.com/symbaroum-resources-page/. As well as the most useful bits from the GM screen, it has a list of common situations and suggested
[attribute <- attribute] combinations. Worth downloading the Unofficial Symbaroum app as well, it's great to have a full list of Abilities, Powers and Monstrous traits in one place for reference - we play online, so having that on a separate screen is a godsend for me.
One thing that I have found, which is more likely to crop up the more you play is that a lot of the Abilities and Mystic Powers are described quite vaguely, which can be confusing if your group is used to quite prescriptive systems. Taken as written, some powers like
Bend Will,
Maltransformation and abilities like
Strangler can end the most carefully planned encounter quite quickly - so you may need to work out a few things at the table as they crop up. For instance the ritual
Possess explicitly states the victim can't be made to commit suicide, but neither
Bend Will, nor
Enslave has that explicit restriction. Perhaps Magic has been made very powerful (unbalanced?) because the Corruption mechanic means that PC casters probably won't be able to get away with throwing a lot of spells around, but often they won't need to. In general my players have been pretty happy with the limits that we've agreed, but none of them has taken any really problematic powers so far (or maybe lack the imagination to abuse them
)
The most important advice I can give though is -
have fun with it. I love playing in a new setting, where everyone
hasn't memorised the Monster Manual
(tm) and you can genuinely instill a sense of mystery and wonder in your players. My players have learned the hard way that there are things in the forest that you can fight and things that you need to run from and I have had them genuinely panic a few times when a creature has done something unexpected or they've realised that they may have bitten off more than they can chew. That said, in 6 months or more of play only one PC has actually died, although that encounter was maybe 2 lucky dice rolls from turning into a TPK.
Hope that helps - Happy to kick around any more specific questions that come up.
And I hope you enjoy your time in the forest as much as we have.