A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
Is The Impregnable Fortress of the Crab's "Your Crab Clan Personalities have +1F while opposed." a force bonus. Does Hida Saiyuki get +2F while opposed with this Stronghold?
Does a personality gain a force bonus when they are equipped with a item that grants a +xF bonus? Does Hida Saiyuki increase the force bonus items equipped to him and if so for how long?
Is The Impregnable Fortress of the Crab's "Your Crab Clan Personalities have +1F while opposed." a force bonus. Does Hida Saiyuki get +2F while opposed with this Stronghold?
Yes, the stronghold and Saiyuki work in the manner described.
Does a personality gain a force bonus when they are equipped with a item that grants a +xF bonus? Does Hida Saiyuki increase the force bonus items equipped to him and if so for how long?
No, because items do not give bonuses or penalties any more, they're just modifiers and Saiyuki doesn't interact with them. Comprehensive Rules, pg 10 (Items)
[...]Items have a Force modifier in the upper left hand icon that directly raises or lowers their Personality’s Force. Items likewise have a Chi modifier. These modifiers are not bonuses, but affect their stat in the same way as bonuses do