When adding new levels of an existing class or adding levels of a new
class (see Multiclassing, below), make sure to take the following
steps in order. First, select your new class level. You must be able
to qualify for this level before any of the following adjustments are
made. Second, apply any ability score increases due to gaining a
level. Third, integrate all of the level's class abilities and then
roll for additional hit points. Finally, add new skills and feats.
The order of how you level matters. You're allowed take a feat the same level you gain the prerequisites only because gaining feats is the last thing you do. If the prerequisite is a skill, spell, or ability, you already have it by the time you take the feat.
Of course, if the prerequisite is another feat, you must already have the prerequisite feat before you can take the desired feat. However, since character advancement is an ordered process, if you gain multiple feats in a level1, you can choose to take the prerequisite feat first. You can now take the desired feat.
In your example, you can take neither feat first since neither feat has its prerequisite met.
1 Class abilities that give bonus feats give them at the time you normally add new feats (after skill points). It's unclear if you choose your standard feat before your bonus feat or vice versa, but I would generally allow players to select feats in any order if it matters.
If you are not bypassing the spell prereq for the item, you are forced to 'cast' it.
From the creating wonderous item section (similar text can be found in almost all other feat specific sections).
If spells are involved in the prerequisites for making the item, the
creator must have prepared the spells to be cast (or must know the
spells, in the case of a sorcerer or bard) but need not provide any
material components or focuses the spells require. The act of working
on the item triggers the prepared spells, making them unavailable for
casting during each day of the item's creation. (That is, those spell
slots are expended from the caster's currently prepared spells, just
as if they had been cast.)
so in your case, each day you spent crafting the belt, you would need to use a copy of the scroll or have someone around who can cast it for you. Otherwise, you have to add +5 to the DC of the check.
Every class that grants a bonus feat should specify whether or not you need to meet the prerequisites. Usually, if you get one specific feat, you don’t need the prerequisites; if you get to pick off a list, you have to meet the prerequisites of the one you choose.
If a bonus feat specifies that you do not need to meet its prerequisites, that effectively changes the feat for you so that it does not have prerequisites. You can have it and use it without them.
If you do not meet the prerequisites of a (specific) bonus feat that requires you to meet them, then you get it but cannot use it (because you must meet a feat’s prerequisites to use it). If you do not meet the prerequisites of any of the feats on a list of bonus feats, then you get nothing (because you must meet a feat’s prerequisites to select it).