Alright, so the way I understand it is you're taking a relatively average shinigami and wanting to use pure swordsmanship as his primary skillset, if not his only skill.
He's got average reiatsu/reiryoku, so he doesn't have lots of stamina, which means every action ought to be very cost effective.
He isn't more tough than the average shinigami, so taking damage is going to suck, but he'll be able to keep on going either through sheer force of will or through some ability--is what you seem to want.
He has no range, so no sword slashes coming off of his blade. Got it.
No keeping up with people's superior speed via shunpo either.,
So the "build," you're going for is Sharp intellect, Master swordsmanship, Base shinigami physicality, and Expert Hoho(I imagine good footwork, more than the use of shunpo from what you've been saying).
Gotcha.
If I wanted that, I'd describe his reiatsu as average, but state it was spread out over a larger distance. Not only would this actually make his presence more faint, but it would also allow him to better detect the movement of other people through the reiatsu allowing him to better track people's actions even without being able to see them. It gives you your 360 degree field of perception (not vision), and something akin to "danger sense," without making it a zanpakuto ability, or sounding more powerful than it is.
(Trust me, I understand your situation well. I posted up Majime and while people seemed to think he was "Captain level," or OP, including yourself, I assure you that if you can close the distance, which is very possible, he's more or less screwed or has to risk hurting himself to properly defend. Putting all of your skill in one area is a risky choice, but still a viable one if done right)
Furthermore, I'd maybe write out a sample or two, exclusively for yourself, of Toshiro in combat, perhaps one fighting a ranged combatant, and one fighting someone up close. You'll get a "feel," for his Fighting Style, which will probably inform you a lot as to how this will work out for you.
Moving on. So you want to not get one shot/totally wrecked by people's various abilities? This is a slightly more difficult issue, as you've brought up, but making yourself basically immune to those abilities, while it does make people have to fight Toshiro with less ranged/elemental/energy-based means, also happens to take away a lot of agency in regards to everyone else's characters--which is why (If I understand Axel properly) you got called out for it by a GM.
What I would do is make his zanpakuto a melee/physical type, with a focus on defense. Maybe it doesn't ramp up the amount of damage he can take, or even create a shield around him, but perhaps it amplifies his sensory abilities, allowing him to better evade such attacks--though doing so will still require exceptional skill and positioning--which is his focus anyways. Conversely, you could say that it makes his body an extension of his blade, rather than his blade an extension of his body. By this I mean he might be able to deflect, parry, and block attacks as if he were a sword. It could also reduce his body's weight and/or allow him to redistribute his center of gravity.
Someone fires Byakurai at him, for example, and he could choose either to slap the flat of his blade against it, deflecting it to the side, or he might use his hand and forearm to strike it and it would cause the same effect that his blade would. Plus, a zanpakuto is typically pretty goddamn durable, so it might not make his own body as durable as someone like Mirja, or Kenpachi Zaraki, for example, but it would very well give him a better chance of defending himself against, not to mention countering, various forms of attack. You could also give him exceptional control over what "little," reiatsu/reiryoku he has, allowing him to perhaps exhale small amounts of spirtual energy or refresh his body with his internal reiryoku, to purge poisons over a set amount of time depending on the effect of the poison and its strength (how fast acting it is).
All of these, while they could be considered exceptional skills, do fall into the realm of the "average shinigami," who happens to be able to use what they have cleverly.
Hopefully some of this helps.