With regard to 1), the personal representatives usually agree with the trustees as to what assets might constitute the trust, although, technically, it is a decision of the PRs and the trustees should accept what they are given. I would be wary of using the date of death value, as the assets should be re-valued for the purposes of the appropriation as at the date of the appropriation (Re Charteris 1917). A half share of the property might be valued as a half of the entirety value for IHT purposes, but for the appropriation you are looking at the market value of the half share alone and a discount should be applied (as though for CGT purposes).
As regards 2), I see no reason why the deed of appointment cannot be used to direct one asset into a FLIT and the remainder of the trust fund absolutely to the surviving spouse, provided the deed is executed by the correct persons and under the correct power. I would caution against specifying a particular value for the “mop up” appointment to the spouse, in case there is any income or capital appreciation that falls outside of the appointment and, therefore remains within the NRB trust. I believe it would be preferable to specify the property interest and appoint the “remainder” of the trust fund to the spouse.