First off, Welcome 😁🖐
(Sniped by Rostok 🤣)
The Double Eagles are well regarded by many members here (I don't have one) so any of them is probably a good choice.
Someone with more experience with them will likely comment further but I believe its really down to your personal choice for the look and metal vs polymer.
Longer shooters are less suited to the sneaking around play style but it can still be fun.
Longer barrels can be beneficial over much shorter ones but only up to a certain point so don't let that influence you too much.
Ideally you want to visit a shop to handle a few different things to feel the difference between metal and poly.
Keep around £100 for LiPo batteries and a decent charger. (Several threads about choosing batteries and chargers)
And the eyepro, boots, camo, pouches, mags, vest, sidearm, holster, smokes, grenades, BBs ........ 😉
Found THIS thorough video testing barrel length. Still inconclusive...