WE try to avoid soft solder in vacuum, but for you, the green or grey GOST standard parts with the hermetic glass are a winner. I'm assuming you do not want to pay 250-350 USD for a commercial feed in KF or other flange. Silver solder is OK. If you want to permanently seal your device, other means must be taken, but for a beginning high vacuum person, they are probably far better then anything you can make, short of Kovar to Aluminosilicate glass or Tungsten to 3320 to Pyrex. . Avoid thermal shock to the seals. They will limit your anode voltage, but for the grids, cathode, etc, not too shabby.
If this is an older turbo, you might want to ensure it has the proper lubricant. A manual for the Turbo is a must, as is the proper cooling. J. Melson is right, a screen over the turbo is a very good idea, because otherwise your setup has to be perfectly clean with no broken parts ever. One thing I insist on is a TC or other gauge right at the roughing pump feed on the turbo. I watch mine in real time and have an alarm set up. You'll hear the turbo "load up" if there is a leak, and if the controller is any good it shuts the Turbo down if it senses drag. Suddenly loading the Rotor is not a sound I like to hear, so be careful.
There are a couple of types of electron gun, some need much tighter tolerances, some need amazing curved shapes, and others sacrifice spot size for ease of building.
Enjoy,...
Video gets better at the middle:
https://youtu.be/jHGAnJjnNY0Video CRT
https://youtu.be/MsMsZaSz3FkFor an experimental unit there are other ways without the specialized materials. PS, Please skip the Hf , RF, and PbO steps in the above videos if you try this...

You don't need low melting glass rods to hold your gun together, either.
One other thing for a beginner, never ever trust your glass, always have a tough screen around it to protect you during an implosion. I've seen a few glass things do a pretty good impression of a grenade if mishandled. Always do some stress calculations on that glass, the amount of pressure per unit area when under vacuum is amazing.
Applied Science has some videos you may be interested in. I imagine you want to do something like Auger analysis? Or you'd just like to see a beam?
Steve