So how can one say "more than ... "? Is that amba lá? Or maybe it is already ambela? Or anything else??
According the Ardalambion Quenya course:
Lá is also a preposition "beyond", and as such it is used in phrases having to do with comparison: VT42:32 cites the formula "A ná calima lá B" for "A is brighter than B" (literally "A is bright beyond B" – notice that the adjective calima "bright" appears in its simplest form, with no ending corresponding to the -er of "brighter").
From what I saw and IIRC, ambë can be used for comparison, but I'm not sure how.