It’s good that you’re thinking about bloodwork and side effect management before starting. That’s already better than a lot of first-time users. That said, you’re focusing almost entirely on the cycle and almost not at all on whether a cycle makes sense for you.

Before anyone can tell you whether 250 mg or 300 mg is appropriate, there are a lot of questions that need to be answered:

How old are you?
Height, weight, and estimated body fat?
How many years have you been training consistently?
What’s your current diet and calorie intake?
Are you bulking, cutting, or maintaining?
What are your current strength levels?
What do your pre-cycle labs actually show (CBC, CMP, lipids, liver/kidney function, estradiol, prolactin, testosterone, SHBG, etc.)?
What’s your blood pressure?
Do you have any family history of heart disease or other cardiovascular risk factors?
What are you hoping to accomplish from this cycle?

Without that information, nobody can intelligently recommend a dose.

To address the support protocol:
I’d also question taking medications just because everyone else does.

Telmisartan: Great medication if you actually have elevated blood pressure or another indication. If your BP is consistently 115/70, why are you taking a prescription antihypertensive? Monitor your BP and treat an actual problem rather than assuming you’ll have one.
Citrus bergamot: Reasonable if your LDL or ApoB are elevated, but if your lipids are already excellent, it’s not automatically necessary.
Fish oil: Makes sense if your diet is low in fatty fish, but it isn’t a magic side-effect preventer.
hCG: There are legitimate reasons someone on TRT may use it (such as preserving testicular function or fertility), but whether it’s appropriate depends on their goals. If fertility isn’t a concern, the decision is less straightforward.
Cardio: This shouldn’t be part of a “cycle support protocol.” It should already be part of your training year-round.
the dose question: As for 250 vs. 300 mg, the difference is only 50 mg/week. That’s unlikely to be the determining factor in your results. Your nutrition, training quality, sleep, recovery, and consistency will have a far greater impact than that small difference in dose.

I’m only on trt doses and haven’t ran a full cycle yet. Also not the most knowledgeable, so take what I say with a grain of salt.

But why question the difference between 250 and 300mg? You could do both over time. Do 250 first for a couple weeks, pull bloods and see where you’re at. If you’re still making progress at 250 I feel like there isn’t a point in bumping up the mg, especially if health markers are in range.

If you stall on progress and your sleep food training and recovery are dialed then consider upping doses. I’m sure someone more knowledgeable on the topic can provide a better or more full answer, though.