It is OK to start low - just a bit of a waste.
Not sure what you expect your body to 'do' - just as i never understood statements such as "assess one's tolerance for testosterone"... But yes, you can.
Just don't start at a dose of 50mg E3D - for one the frequency is too... infrequent, and for two the dose is far too low.
With Testosterone 'PROPIONATE' it takes a certain time ('decided' by the propionate ester) to leave the injection site, by three days more than half of the hormone has been 'used' and as such injecting every three days results in large variations of hormone levels increasing side effects. It is better to inject a smaller amount more frequently than a large amount less frequently - this goes for most AAS i can think of.
As for the dose being too low... 123mg/wk will be enough to suppress your natural production but provide barely more than you made naturally - making it a pretty futile exercise. HRT is Hormone Replacement Therapy and is the most common medical use for Testosterone drugs. You don't want to merely replace your Test'rone,. you want to super-size it!
If you start 'low' start at 30mg/day (280mg/wk) and increase weekly by 10mg a day. So week 1-280mg, week 2-350mg, week 3-420mg, week 4-490mg, week 5-560mg.. and if you find a dose you like (i recommend 490-560mg) then you stay at that until the end - don't then drop the dose down. If you want to inject less frequently then inject EOD - no less.
Let me repeat something so you know where i stand with this though - i think you should go in at the dose you are going to use throughout the cycle AT LEAST, with my preference being to frontload the dose actually.
I would suggest you use Anastrazole throughout the cycle - it's dose depends on what dose of testosterone you use - so that's gonna be a pickle ain't it?! (I'd suggest approximately 0.25mg of Anas. per 250mg of Test'rona - as a rough guide).
An AI isn't overkill with Mesterolone simply as Mesterolone is not doing too much anyway. It is not an AI. It is an AAS with affinity for the Aromatase Enzyme, these are two very different things my friend.
If you want to keep side effects low - this includes growing tits - use an Aromatase Inhibitor at the correct dose. What you choose to do with the proviron is of little consequence - it will improve your look though even as high as 15% bf IF you have a decent amount of muscle (you don't sadly - sorry).