starter relay needed? ????

What you are thinking of doing is IMO fine, but kinda defeats the whole purpose of having a relay. The oem relay is under the hood, between the battery and the starter, to provide as short a wire run as possible, to deliver as much current as possible, with as little heating as possible.The starter solenoid does draw a considerable amount of juice.
By bringing that current into the cabin, you are creating a much longer wire loop, and bringing an unfused high current wire through the firewall, and into close proximity to all kinds of sharp metal edges.Better it would be to trigger the oem relay with the momentary.That could be a 14 or 16ga wire and easily fused. Your ignition sw will love you for it.
All your other high current devices should be similarly relayed, with the relay wired between the device and the battery with as short a wire run as possible, and outside of the cabin, and either fused or fuse-linked. The trigger sides can then be run off a switch in the cabin and through the Ig,sw. and a fused source.
High current devices include;pumps,fans,solenoids,A/C clutchs,capacitor discharge ignitions and high-powered headlights.
Look under the hood of any modern EFI vehicle. You will find a power control center where all those relays are mounted. The factory is keeping the high-current out of the cabin.
Just trying to be helpful