Camo tape covers a multitude of sins.
£42 MB-03 (you'll be replacing most of it eventually, so why not start cheap?)
https://gunfire.pl/product-eng-1152189623-MB03D.html
£24 tune-up kit (you'll likely need to clip the spring down to hit site limits, same with the £21 kit that is out of stock)
https://gunfire.pl/product-eng-1152199894-Tune-up-kit-for-the-sniper-replicas-MB02-MB03-MB07-MB10.html
£11 6.03mm barrel (currently out of stock, alternatives are available)
https://gunfire.pl/product-eng-1152204578-6-03-steel-precision-inner-barrel-550-mm.html
£25 3-9 x 40 scope (or £30 for the 3-9 x 50)
https://www.ebay.co.uk/itm/162504564225
After clipping the spring down to get ~500fps with 0.2g (get used to taking it apart and clip it a bit at a time if possible depending on your access to a chrono) that'll get you something minimally usable. After that it's all about the hop. The Action Army VSR unit is recommended but costs more than the base gun so I'd leave that for the advanced class. I'm getting on OK with the stock unit and rubber, and a modified Airsoft Pro lever. Mine currently has a curve to the right, but it's a consistent curve which can be ameliorated by rotating the scope. I'll likely sling the stock hop arm back in to see what we see.
All that said, I agree with getting an AEG first. Most of the time, it'll be far more effective. Sniping can indeed be frustrating: you're rarely offered an easy target in your sweet spot where - if you're lucky - you outrange AEGs in a flat shoot out. Better hope they don't realise they can lob bursts at you.
If you get a short M4, slidey-stock MP5, or something similarly handy then you could consider running it as a secondary instead of a pistol if you do go sniper later. Don't get an MP5K though, I want to keep that a secret.