What's your current weight and bf%? How tall are you.
I usually tell people not to rush into using AAS. If you have been lifting for only a few months then I usually tell the bro to wait a while longer. But, the fact that you are 30(I am 40), might make a difference as your body chemistry is declining big time now. Everybody is different, but you need to give a few more specific stats so the bros can make a better determination. Generally, when lifting for less than 2-3 years it is not a good idea to use AAS yet. Just my $.02.
Dbol/letrozole is a crappy non cycle. Don't bother with it. It is cheap, yes, but also inefective and you will lose most of your gains post cycle. It will mostly be estrogenic bloat. As soon as you come off you wiil lose it.
I have a bad back myself. Nothing as bad as yours tho. I have 3 herniated disks from 20 years ago lifting. I would stay away from the winny personaly, although I have used it, love it and suffer no back pains while on it. Dbol will also give you lower back pain. I stay away from dbol as much as I can because of this. It is well kown that most bros get lower back pains from dbol.
Don't use tren and deca at the same time. They can each individually cause progestenic gyno that no anti-e can help you with. Taking them both at the same time is pushing it, and I would rather be safe. I always tell people to use EQ instead of deca if they want to use tren.
Tren is not the best AAS to use for a first cycle because of several issues. For a first cycle injecting EOD or ED is not the thing to do. You need to get used to injecting once or twice a week first before going to more regular shots. Another reason to not use tren is that some shots will give you what is called a tren cough, and this can be quite frightening to a rookie. Hell, it STILL scares the **** out of me. Yet another reason is that it makes you MAD aggressive, and you might push yourself to hard and hurt yourself lifting. I have to hold back when on tren or you start adding 45 lb plates like it is a joke, and then the next day or week your tendons and joints hurt.
Prop is not a good choice for a first cycle either because of frequent EOD or ED injects and the fact that prop is a painfull shot the day after, and it takes a little time to get used to it.
If you still insist on doing a cycle I would go like this.
Week 1-10 Deca 400mgs/w
Week 1-10 Enanthate 500mgs/w
I don't want to tell ou to use dbol the first 5 weeks because of your back but this is what is usually added like this
Week 1-5 Dbol 30mgs/d
You could also jump start the cycle with prop instead of dbol the first 4 weeks like this
Week 1-5 Prop 100mgs/EOD