Welding Tips and Tricks

I am a beginner welder I am trying to get my 3 and 4g certification and want to do a little practicing from home I have a welding machine but don't have some of the other tools I need and I was wondering if anybody could give me some tips on beveling plate without a track torch and what can I use or how to make a weld stand

You can bevel your plates with a grinder. It's hard at first (or was for me anyway) but beveling with a grinder can be done great once you learn how. As for a stand for coupons you can do a lot of things. Do you have just a welding bench? You can make something real quick to use to tack up to the table or if not you could take some pipe or tubing and make a stand like that with a base.

What is the best way to bevel to bevel with a grinder and what's the best size grinder to use

Depends on plate size, but for your purpose a 5" grinder should do the task no prob.
Best way it IMO to scribe lines where you want it to be ground and then put it in a vice and grind to those lines.

Thanks