Here are some directions that might help you move forward
1. Do I need 2 relay nodes?
It is not necessary to have two relay nodes but each stake pool must run at least one block-producing node and one relay node. The block-producing node holds the keys and certificates necessary to issue blocks and rewards payments, but it should not be directly connected to the network because you don't want to be exposed.
For security reasons, it must be connected only to one or more relay nodes controlled by the stake pool operator. Then, the relay nodes connect to other relays on the network. This setup is configured in the topology.json file.
2. Are the server requirements for a relay node the same as those of a block producer?
Officially, the minimum required is the same for a BP and a relay node. However, from my personal experience with equivalent servers the relays consume on average slightly more RAM.
3. For a start, is there a specific pledge amount with no delegators yet, that would have chances of producing a block?
- You need to have 500 ADA for the pool deposit
- It is not a question of knowing if you are going to produce a block
or not for such or such amount of stake/pledge but rather to know how often?
With 100k ADA your pool will produce about 7 blocks per year. You can take 5 minutes to read this interesting thread "Actual Cost to Operate vs Actual Returns thoughts?" on the official Cardano forum.