basically F1 is to see your character window then just click the numbers. it much faster than picking a new gun. what I would do also is pick different ego powers and perk for different set ups.
load outs I would recommend.
1. survival load out: I would have all siphon weapons maybe a healing weapon to. I would recommend fast weapons to trigger siphon more.
This load out is all about getting health back or tanking.
Ego: Any
2. dps or ranged load out: this is really your sniper class as they will do the most damage in general maybe get a good machine gun to.
Ego: overcharge or maybe stealth with damage perks.
3. support load out: healing weapons or have something with bio or radiation to slow enemies.
Ego: decoy is a must here. also grab some revive perks like reviving one ally revives all and recharge shields on revive.
4. Aoe or demo load out: I would use grenade launchers and maybe explosive shotguns or rocket launchers. this load out is just to clear a lot of enemies all at once.
Ego: any really but overcharge again would help.
5: back up load out: anything you need stick it here. maybe use this as a back up survival or dps.