Hi Julia,
I am confident i can help you.
Your husband's testosterone level is low (anything below 500 "IS" low). I am battling with these testosterone issues myself due to head/groin tramua and now suffer low testosterone at 23. I have a similar testosterone level to your husband.
For a man to be fit, healthy and have a good libido/erections he really need's a testosterone level about 650+. TRT can give a man this.
Delayed ejaculation could be due to high E2 levels. How does your husband feel his erections are in general? Difficult to get/maintain? Does he have alot of abdominal fat or problems with flushing?
You mentioned two thing's that got me thinking. Your husband had a vascetomy, this can lead to low testosterone many year's after surgery (though no one will be able to prove or disprove this). The slipped disc is also a sign of low testosterone, it's possible infact that your husband had a much higher risk of getting this due to his declining testosterone level. Testosterone is required by the muscle and bone groups to keep your joints healthy. It's important for all the organs, including the heart.
Any TSH over 2 should mark further investigation. Get total T3/T4 checked and also free T3/4 blood profile done. While TSH is still in the "normal" range it might be causing some of the problems, thyroid has a huge degree of control over libido. It's possible your husband is suffering from hypothyroid. Check out the website [deleted] for further information on this.
Urologist's tend not to like TRT (from my own experience) so you might have to make the decision between yourselfs. TRT has it's advantages and disadvantages like anything else.
[deleted] i can provide more information on any of the above. I need to sleep because tomorrow i am going in for surgery to try and fix my own testosterone problem (varicocele caused low testosterone for me).