Cistern for garden irrigation - Which pump?

Use the fittings from Unidelta. They have all the variants you need, e.g. T-piece. What kind of PE pipe do you have? You don't need a conduit for the PE pipe. Of course, you can connect a submersible pump to it. That's exactly what such permanent installations are for. Again, Unidelta... And it's not complicated either. I have a 63mm PE pipe on my submersible pump. That is really rigid... I guess you have a DN25 or at most a DN32.

I bought DN32 from Controlled Residential Ventilation (Hornbach), T-piece, L-piece from Marley.

1. Conduit, T-piece: the idea of using a conduit is for repair, replacement. If I have a distributor/T-piece in the middle, a conduit won't help. Is it better and simpler to bring the PE pipe with the T-piece directly into the ground (without a conduit)?

2. Connection to submersible pump: I don't have a solution yet for the connection to the submersible pump. The 32mm pipe is rigid, not flexible. And I have to connect it at a 90° angle to the submersible pump. And to connect it, I have to bring the 32mm pipe about 1m upwards.

To connect, use a 90° fitting. Then lower the pump. Then another fitting on top. This also makes it easy to replace or service.
Pe pipe directly into the ground. Certified up to 100 years depending on the PE pipe.
If the KG is longer than a few meters, you won’t be able to get the PE pipe through anyway.

To connect, use a 90° fitting. Then lower the pump. Then another fitting on top. This also makes it easy to replace or for maintenance. PE pipe directly into the ground. Depending on the PE pipe, certified for up to 100 years. If the KG is longer than a few meters, you won't be able to get the PE pipe through anyway.

thank you for your answer. Originally, I wanted to realize it like my 1st plan (see attachment). Here, however, I have to climb down every time (for maintenance, repair) with a ladder. I would rather avoid that.

Thanks to your suggestion, I think it is better like my 2nd plan. Here, however, I need 3 fittings (instead of 2 as in your text). With this solution, I will probably lose a lot of pressure.

Have I made a mistake in my reasoning here? Maybe you have a better idea?

Plan 1. Fitting but not centered as in the plan, rather all the way to the right or even a bit longer. Then the pipe is long enough for you to pull the pump up with the pipe. This way you can also reach the fitting without climbing down. A dn32 is not that rigid. Not even a Pe100. If it's cold, you can warm it up with a hairdryer. Theoretically, you could also just make a bend with the pipe in the shaft without any fitting. Or you use 45° bends. The pressure loss is significantly lower there. Overall, however, one or two more angles should not make much difference. You rarely have to get to the pump anyway. How large will your irrigation system be or what flow rates do you need? Which pump will be used...

Plan 1. Fitting but not centered as in the plan, rather all the way to the right or a little longer. Then the pipe is long enough for you to pull the pump up with the pipe. This way you can reach the fitting without climbing down.
A dn32 is not that rigid. Not even a Pe100. If it’s cold, you can warm it with a hairdryer.
Theoretically, you could also just make a bend with the pipe in the shaft without any fitting at all.
Or you use 45° bends. The pressure loss is significantly lower there.
Overall, one or two extra angles shouldn’t make a big difference.
You rarely need to get to the pump anyway.

How big will your irrigation system be or what flow rates do you need? Which pump will be used...

Thank you. I will try it out to see how well it processes. I fear that despite all effort I won’t be able to bridge the good 1m depth.
I was also thinking about a 45° fitting. I could find very little/almost no offerings (Amazon, Ebay). Do you perhaps have any other tips for me?

Unidelta. Available at Wolf for about 3€. Search for Unidelta 45°.