For the first question :
Actually there is "Dwarf Star Dragon Planeter" That allows you to search for a level 7 dark monster.
For the second question :
No idea what could allow you to tribute summon this guy in 1 turn in a generic deck.
Perhaps "Superheavy Samurai Big Waraji" ?
This guy can be special summoned, then counts as 2 tributes for machine monsters.
To activate the best effect of World Legacy - "World Armor" it must be normal summoned or set.
How do you easily set or normal summon a level 7 (2 tributes) monster to make use of its second effect in a generic way ?
Well, you can use the skill of the Paradox brothers, Three-star demotion.
This skill makes "World armor" level 4 which can be set = No more Fusion/synchro summon.
Since this skill can be used once per turn + "World Armor" returns to the hand your opponent cannot special summon extra deck monsters FOREVER.
The only issue is to get your life points to 1000 or less.
I didn't buy the Future Horizon pacs yet, so no Heavysamurai for me. So as suggested above I tried using Dopplewarrior but I don't know with which tuner and synchro it works better.
Anyone know which Synchro and tuner ?
I do find it easy to get world armor and Dopplewarrior in my hand though. Easy world legacy clash.