Please, I need your advice.

What would be the best modifications to put on an x-wing ship?

Many thanks

Its more a case of choosing pilots that work well together with xwings.

Astromechs can help loads.

For example luke with R2D2 and a shield upgrade is stupidly durable.

Don't waste time on ordnance unless you've got spare points.

Wedge likes predator, gives him a free 'mini target lock'

Tarn Mison - R7 Astromech, possibly a Stealth Device

Hobbie Klivian - R3-A2, 2nd option would be R7-T1, or R7

Biggs Darklighter - R4-D6 - Shield Upgrade

Garven Dreis - R2-D6, Veteran Instincts, Biggs Darklighter so he can have 2 focus tokens

Jek Prokins - Ehhh... R5-D8, PTL, Hull Upgrade

Luke Skywalker - R2-D2 (R5-P9 if using Wedge), Lone Wolf, Engine/Shield Upgrade

Wes Janson - R2-F2, PTL, Stealth Device

Wedge Antilles - R2-D2, Predator, Hull/Shield Upgrade

I'd go for BB-8

R2 Astromech.