There is a lot of advice and opinions surrounding each one of your points lol. You'll end up inundated with advice.
Instead of giving different views of methods I have seen. I'll just tell you what works for me. That of course doesn't make it the right way or the only way to do things.
Ways to hold mini's.
Depending upon what model I am painting and how I am painting it.
I have used wine bottle corks, if I have drilled and put pin in the bottom of the model. You then just push the pin into the cork. Now you can hold the cork so you don't touch the paintjob (not done this with X-wing models yet).
The tops off aerosol cans attaching the model with Blu-tac. I usually do this with models that are attached to their base. However I have used this with X-wing models, just pushing the peg into Blu-tac. I wrapped masking tape around the peg to protect it from overspray, maybe you won't need that.
Of course you could just use the standard base too.
I also used to Blu-tac based models to paint pots I wouldn't be using.
Well if you type paint palette into Google you'll find loads. I have a round plastic one that cost about £2 from a craft shop. However I mostly use the blister pack that my models come in as palettes.
I also own a wet palette, made by Privateerpress. I have also made a wet pallete from a model's blister pack. A long time ago I used cheap white wall tiles.
I prefer using the blister packs because I don't have to clean them, just throw them when they're full.
The brushes currently lined up next to my paints are from 3 manufacturers.
2 Rosemary & Co. Already linked above.
1 Formula P3 base hobby brush.
One or two brushes from the basic Wargames Foundry set.
I think the brush descriptions will tell you what I use them for, losely.
As I have an airbrush I don't use brushes to varnish. But when I did, I had separate brushes for the sole use of gloss and Matt varnish. Just bog standard nylon brushes, nothing fancy.
I would recommend any of those brushes above. Especially Rosemary & Co. Excellent brushes for a good price.
I use Army Painter sprays. They have a large selection of different colours. Are cheaper than games workshop. I have not had any issues with them. I am in the UK so rarely does our climate cause problems.
Although I have also used Halford mat car primer before too. Which you get more of for you money. I just found a bit more care was required with that though.
I also use Vallejo Surface Primers too. Admittedly with an airbrush, but you can brush them on too I believe.
I currently use paints from the following ranges. Formula P3, Vallejo (model, game, and air ranges), Wargames Foundry. I have been painting for a long time now and so have ended up with a fair selection of paints. Others include Coat D'Arms, Gwames Workshop, but not many. If you know what colours you want then shop around. If you're after starter sets then I would recommend the P3 starter sets. I like P3 paint, and if the sets contain the colours you're after then they offer a good discount over individual pots.
I probably use mostly Army Painter soft tone, strong tone, and dark tone inks for my washes. I also have P3 inks and some old GW stuff. I have tried Vallejo washes but didn't like them, they dried with a white residue. I keep meaning to try some Secret Weapon washes though.
The previously mentioned brands all have suitable metallics. For gold I think I prefer Vallejo Model Colour Old Gold. Silvers I find P3 and Foundry to be similar. Although I highlight with a 90s pot of GW Mythral Silver, closest equivalent would be Coat D'Arms Enchanted Silver I think. P3 have an interesting colour with Radiant Platinum, which I do like a lot.
Water is pretty much all I have ever used.
I have no experience with aerosol varnish.
I do use Vallejo mat and gloss varnish with my airbrush. Before getting that I painted it on by brush.
The Internet is flooded with model painting articles. This single link covers a pretty wide array of stuff, and is only the tip of the iceberg. Must be a pretty big iceberg eh
Not a mixing chart as such, but a shading and highlighting chart for P3 paints which I have found useful.
A sharp sturdy craft knife is all you need for X-wing models I reckon. I use an X-acto craft knife, random Googled link. I also have a cutting mat, saves the desk or kitchen table.
Right that's all I can be bothered typing now, hope it is of some use.