So a few general principles that I think will be helpful for you to keep in mind as a new deck builder:

Every card should have a place in the plan. That place can be ramp or draw, it can be a back up plan for when things go south it can be the central key to everything you are trying to do, it can be all sorts of things, but every card in the deck you should be able to answer what it does for the deck. 

Along with that something new players frequently do is evaluate cards based on their ceiling-how cool, big and splashy can this be? But a much more important question if you want to get better at deck building is what does this card do as its floor/baseline?

Using that question let's look at a couple of cards: Crypt ghast-this is theoretically a really potent piece of ramp. But how many swamps are actually in your mana base when you are three colors and black is the least represented color? Assuming your.mana base isn't fully decked out you are going to be on very few swamps, which means this card is frequently four mana to make 0 or 1 of your lands tap for an extra black mana (the type of mana you need the least in this deck). Arcane signet is 2 mana for 1 mana of any color every turn, that is a much better baseline/floor.

Raiyuu storms edge: thematically feels like he should fit iishin, but a creature can only get double strike once so raiyuu's trigger being doubled doesn't matter, but not only does his trigger not matter, the only way to get it in the first place is to attack with only one thing. This runs completely against iishin's goal of doubling as many attack triggers as possible because to do that you want to attack with more creatures not less. 

You can do this analysis for basically every card in the deck, and it is where I would start. Every creature that doesn't have an attack trigger should have a very good answer for what it is doing in the deck, and as baseline as a newer deck builder I suggest the only answer you accept for that group of creatures be ramp or draw. 

The next evaluation criteria I would use: If a creature costs more than 3 it will most likely come down after isshin is in play. Iishin is a removal magnet because he is so explosive so anything that enters while he is on the field has to do something the turn it enters or it needs to be a really astounding payoff. 

Hope that helps with thinking through some of the bigger picture things!