Everyone is on point that right tube is very critical. Ps. If you are buying cheaper tubes on eBay or Chinese market place than there are some modifications you can do at the base with hot glue gun.
Putting a layer of hot glue at the bottom helps with it cutting into your bone by releasing the tension (more expensive glass cylinders already have wide extension on the bottom of it which helps to spread out the tension). Put it on outside and on the edge so it doesn’t put too much pressure on your skin. Put it on flat surface and go around it couple of times (than cool it). If you make a mistake just cut it or heat it with either a hot air gun or something similar (which will soften it up again and become more even).
2" diameter is good start for anything in range of around 5.75-6.3". Problem with getting 2.25" too soon for up to 7.1" circumference is that you might have your large veins/testicular tubes being sucked in to fill the space and can definitely lead to a lot more problems quick. Also, you are focusing on the head and not further girth so 2" is good or 2.125" of you can find it. But 2" will help with straightening your penis (2.25 would help with straightening yet).
Also, I started to kegel while I pump to have better results. Kegeling technique can be researched but basic is 2-5 seconds pushed in, 2-5 second pushed out (I don’t know the terminology so research it for better techniques). Don’t more rather than less level is better.
Things to watch out for, veins popping and blood spots in the skin (it’s an indicator that you are pumping harder than needed, or your body is not ready for such a suction yet). Most of them go away between 24-48 hours, but could be a potential high problem if not careful.
Also, ring of fluid build up between shaft and glans (also related to over pumping in general, but it’s a slightly less traumatic experience). It goes away anywhere from 15 minutes to 24 hours depending on your body.
Don’t be eager to start hard and strong, take it easy, you only have one penis.
Huge plus, proper jelqing for 15-30 minutes a day bring far better results than pumping alone. Pumping more or less is for better blood circulation, although some people see mild results (0.1-0.3" increase in size over a year spam compared to 1.0-2.1" with proper and safe jelqing). Unless you are trying to stay the same girth, jelqing is a must with any other techniques for best results.
As far as straightening out your penis and increase size than traction device with jelqing is better choice. Cheapest traction device go to $15-$20, let me know if you need advice there too (there is one you want to avoid because of poor quality).
Tract your progress and keep us posted if you have any more questions.