Part of the information problem is that much of Imbuing is still "shaking out". As soon as we have it down, they make balance changes in a publish, and half the previous information becomes obselete.
1. Start with exceptionally crafted normal leather, made with runic kits. They removed the caps (And boosted the low end) on runic intensities a couple years ago. While stuff crafted with normal tools has higher base resists, due to the higher Exceptional bonus, that is somewhat negated by the fact that a resist property can only be imbued to 15 higher than its normal leather base resist (so if you had an item that was 3 base resist in an item, then got 5 more from the ex bonus, and 12 more from a runic property, trying to imbue it would make it go DOWN 3). What you want to shoot for is your desired non-resist properties coming in at 100% intensity from runics, use POF to get to 255 durability, then imbue the resists you want. Then, once you get a few of these, attempt enhancing with your leather choice until one succeeds. It might take a while, but tailor runics are cheap, and the items to imbue resists even easier to get. Note that Self Repair on an item goes away if you imbue an item, as well.
2. As with the tailor runics, making exceptional weapons with runics, using iron ingots, is the way to go. Elemental damage no longer counts as a property when imbuing or runic crafting (so it's possible to get it, plus two more properties, with a shadow runic, for example). Shoot for near-max in the properties you want with the most expensive imbuing ingredients, so you don't have to imbue them. POF up to 255 durability, and imbue the rest (And remember that you can lower DI with imbuing, if you need to make room for raising another property).
3. As noted before - runic made exceptional, with the expensive properties already present before imbuing. For Armor, especially, you want items whose resists are near-minimum in the ones you want to imbue, as that means that more of the Arms Lore & regular exceptional bonus would be retained.
If you have a piece that's 6/10/4/3/3, if you imbue it with 15 physical & 15 fire, you'd only end up with 17/19/4/3/3, and lose 10 of the 11 bonus resists, and have 46 total resists.
If you took the same piece and imbued 15 poison and 15 energy, it would end up 6/10/4/18/18, not losing any of the exceptional/arms lore bonus, and having 56 total resists.
Note that material (leather type) bonuses are also replaced this way as well, so that's why it's worth making several pieces, then gambling on enhancement after the fact, so long as you can supply yourself with your own POF to use before imbuing.
4. Yes, you can use bought jewelry (as jewelry doesn't have -50 penalty to max intensity of armor & weapons), or you can make recipe jewelry to use as the base.
5. Yes, you can put skills onto jewelry. But, be aware that skills come in 5 groups, and you can only have one skill from each group (look at the sticky with the skill groups
here ). If you try to imbue two skills from the same group, the new one will replace the second.