Which juristiction ?
e.g. EASA Ops has raised the requirements for freelancers to be operationally fully compliant (Full Operators conversion course etc.) so it is actually not so attractive any more to hire freelancers. This also implies, that even if your training is up to date, the company will have to cover all your training again and also send you to the Sim for an OPC followed by line training as specified in the OM-D - as you are experienced on type, this can be probably be done in 5 Sectors. (As for the OPC - I know some companies do it "on-type" - but it is cutting corners to save - what ?). With NCC-Ops manifesting itsself, these requirements will also start playing a role in Non Commercial Complex operations, although probably not as stringent.
Depending on where you operate and your home base, you will also have to charge VAT for your services rendered on top of your normal income tax. A good tax consultant may proove very useful !
When I do the math - freelancing is not really worth it in Europe any longer if you do things legally unless the services you provide are indispensible and extremely sought after - is this the case as a F.O. ? Normally experienced TRE Captains's for G650 etc. are more likely to be in those kind of positions.