Team building

[Lord Windos]

I have chosen Gararewl to wear down opponent's Nucleon due to its Steel typing. So, I prefer a Pokemon which resist to ground types. I take Choice Scarf Pajay to outspeed Nucleon and others Pokemon.
Is it a good idea ?

Good enough idea, but having a Pokemon that is 4X weak to Stealth Rocks with not a lot of bulky is asking for trouble. Their's no shortage of Hazards in Uranium, so unless you invest in anti Hazard support the phoenix isn't going to be surviving for too long.

Another option to take is going with With a Speed Nature Choice Scarf Technician Alpico , as they are one (If not the most, outside of Priority and Inflagetah/Archilles) of the fasted Pokemon in the game than can handily take care of Ground and Fighting types that would waylay Garawel/Feliger, and do a dang good job of nuking all the Dragons besides Bulkly Tracton, destroying Gliscor, and blighting Mega Sableyes. 

Chlorophyll Coalith with Sun Support is also fantastic for outspeeding everything depending on how you invest in it and blasting them away with Nasty Plot boosted Solar Beams/Dragon Pulses/Earth Powers etc., though you have to beware Ice Sharders or the likes of Bulky M-Arbok and Metalynx ruining its fun.

Final Pokemon you could consider is Seikamater. She's all around very Bulky, can learn Sticky Web or Tail Glow from Sponee and Triwce respectively, and has access to 5 STABs thanks to Elementalist, giving her a supreme amount of flexibility and power with her Movesets. Best combo for support/Defense would be Sticky Web or Quiver Dance/Heal Order or Quiver Dance/Ice Beam/Thunderbolt with Leftovers on her I think, but hey, experiment to see what you think is best!