JK, of course test will promote a lean muscle gain, it will improve recovery, improve protein synthesis and nutrient partitioning, and enhance the stimulus to your training, thats what it is intended to do.
I am not going to try to act like a steroid expert, because I admittedly am not, but compared to what the body produces naturally and is intended to produce naturally, 250mg is still an enormous amount of test (relatively speaking). So, I agree with everybody that you would shut down natural production of test even wit ha moderately doesed cycle for a moderate time period, and even with proper PCT, at this point, the last thing you want to do is screw with your body's own natural processes that you already have with the starvation diets and overtraining. I still think you should wait it out, you're only on week 2 of this program, man, I understand you'd like an 'insurance policy' because you still have a fear of getting "fat".....but you need to truct what you're doing and trust your body, you're a 30-year old guy who is grossly underweight, but you're in perfect health, your body can and will put on lean muscle for quite some time, just let the body return to normal functioning, give this a couple months, see what your gains are and re-evaluate then.
Also, Cyp and Sus aren't interchangeable, you'd have to plan differently depending on which one you took, and to my knowledge and from my experience, Cyp would probably still be in your system 2 weeks after the last shot to some degree, and you wouldn't even benefit from it until after the second week of the cycle sometime. And with Sus, the fast acting esters make up roughly half the drug (I think), so you need to look at how much will be in the system and for how long.....again, the two aren't interchangeable with one an other one doesn't work like the other.
What you outlined would probably work better in theory with Propionate or Suspension, something that gets in, does its thing, and gets out.....in that case, what you're thinking makes sense logically, but, with long-acting esters, it isn't that simple......I would really just chill out and eat and train and sleep and just have faith that your body will normalize, because IT WILL....at 30 years old your body is far from drained and old, it will bounce back. It took you 4 years to wreck yourself, it certainly won't take another 4 years to get back, but it will take longer than a week also, just be patient and enjoy the ride.