Welcome to the Right place and Right time- UG is a great community and posting an intro is a big part of being a part of the “community”
In terms of a cycle, 20 weeks on your 2nd run might be a bit long. You could see some diminishing results running just test @ 500 a week going into the last weeks of a 20 week run. 12-16 weeks is probably the longest I would consider a cycle if I was not on TRT. I also would not run straight Test E for 16 weeks. I would add an oral or something like Deca with it. That’s just me- others will say different.
Using 300 mg of Test alone isn’t worth you shutting yourself down. Running lower dose Test for longer also doesn’t make a ton of sense if your goal is size. You would be better off running Test @ 500mg /week for 10 weeks than 300mg/week for 20 weeks.
Anavar isnt a “bulking” drug really. Obviously diet and training dictate results not the compound but certain chemicals are more suited to certain functions. If you want to bulk run Dianabol with your cycle for 4-6 weeks @50 mg a day to kick start and you will blow up, if you train and eat!
When I plan a cycle the first thing I plan is PCT- not AAS. Price out your preferred PCT- clomid, nolva, HCG, etc… The next thing is supplements like Cialis or Proviron (actually a steroid), SARMs, and so on. The last thing I plan is the AAS. I find that PCT can be as expensive as the cycle depending on gear. In your case PCT will cost double the gear you are using or close to it. I mention this because you have no PCT mentioned but do have Osterine.
Good luck and keep reading, researching, and asking questions.