I’m just beginning with mead but here’s my understanding... you could go either way with blending. Some flavors diffuse better in water (if used in your mead) ahead of fermentation when there is no alcohol, and some better in alcohol (afterwards). I imagine some of it is your preference for taste and some of it is also how you practice.
Back-sweetening is something different, although you can impart flavors and taste depending on what you use to back-sweeten. For example, I can use honey to bring up the sugar content of a wine prior to fermentation to get my SG up to 1.090. During fermentation, some of the flavors may not come through the other end based on type of yeast, temperature, nutrients, etc... so I will typically use sugar to bring up the SG in wine, and back-sweeten with honey to get the amazing flavors of the honey. Use potassium sorbate after fermentation and before sweetening or fermentation could start again just as you would with wine. Another way to keep it sweet is to have more sugar than your yeast can ferment (a higher SG) and so not all the sugar gets turned into CO2 and alcohol. I don't have experience with this method, however, so someone else will have to chime in.
In terms of degassing, just like in wine making, yeast will produce CO2 and alcohol and so it's quite similar to that regard. Same with clearing. I've used bentonite in all my ferments for clearing, and as I've read here to give the yeast a place to do their work. It has worked quite well for me in terms of clearing both wine and mead. I've been reading lately that it's not so important to degass so quickly as the CO2 helps to protect the wine / mead if you're cellaring it for a length of time. Plus, as I understand it, the CO2 helps maintain some acidity, which helps potassium metabisulfite protect better at lower levels, and it helps protect any head-space issues. If you're bottling sooner, it's best to degass.
I've heard that the longer mead sits the better it is. I'll say that for the first mead I made this is very true.
@dmw_chef helped me with understanding nutrient addition and amount of honey to use up front and the second mead I made didn't last 6 months.
@BernardSmith is also a meadist with a lot of experience and I believe
@winemaker81 is as well.
I bulk age in carboys until I'm ready to bottle. I'm suspicious of bottling early, in that it seems like a ploy to make more. Unless the ploy is by my wife and not someone selling me something. LOL