I have been thinking about this recently, what Will happen if Bitcoin network gets too big? Will there be any issues with it's speed or fees
It can cause network congestion, mempool overload and higher transaction fees but there are solutions like Bitcoin Lightning Network, and layer-2 solutions.
When you are more knowledgeable and experienced, you can plan and choose good times to consolidate your small inputs with fee rate and also make your transactions on-chain with cheaper fee.Bitcoin layer 2 resources.Sidechain Observer - Bitcoin L2 Projects & current state of development.