You want your bolt to close on the "go gauge" but not the no-go gauge. If it closes on the "field" gauge, then you've too much headspace and need the barrel set back a bit. Your gunsmith can do this for you. It's actually easy, but if you do it yourself, you should remove the extractor from the bolt (which isn't hard either).
Repro sniper scope should be compatible with the scope mounting system you buy. Be advised that a lot of these repro scopes and mounts are made in the Workers' Paradise.