Descale after hot bending and welding. Where possible place before filter, not after. Use O-ring fittings rather than tapered thread type. If tapered fittings cannot be avoided, use liquid hydraulic sealants rather than teflon tape. The cheaper, low pressure element is many times larger and has the potential to filter continually and under more ideal conditions.
Oil is compressible and can often limit servo response.
As a rule of thumb they decrease stiffness to a third of that of the volume of oil they contain. Additionally they produce contamination which must pass through the servovalve. Use only nylon, teflon or thermoplastic lined hose. Remember, to control flow the SV must drop pressure across itself. Too large a valve is a waste and worse than that, it lowers system resolution.