Level links will get you level or whatever height adjustment you like. If you read up, the air system can throw errors if you go too far up or down from stock setting. I haven't had any issues with mine so far. I'm set within 1/4-1/2" level.
If you add just the spacer, it won't get you level as the stock links will just cause your bags to deflate and get back to stock height. This could throw errors being underinflated. If you add just the links, it may be a little bouncy, but it seems it's just preference to some if they mind or not.
My combo is a Daystar spacer on top of the front Air Struts and utilization of some adjustable links. As far as install on the spacer, it was the same as any other truck with a few added notes. Drop to entry/exit, set air system to tire jack mode, disconnect battery, disconnect brass air fitting on top of strut and keep clean. Other than that, it's just your normal remove upper ball joint nut, lower tie rod joint, sway bar link, strut bolt, and upper strut bolts. On a clean new truck, it's about a 3hr job.