This may be jumping the gun, but I was thinking about 400 point Imperial builds that can be made using Wave 1 materials. Feel free to add your own ideas.

Since many people will end up with 2 Victories and 2 Gladiators, I decided to try to build a list around using all 4 of those ships. Here it is in all its 400 point glory:

Gladiator I @56 + Demolisher @10 + Engine Techs @8
Gladiator I @56 + Insidious @3 + Expanded Launchers @13 + Engine Techs @8
Victory I @73 + Screed @26 + Enhanced Armament @10
Victory I @73 + Enhanced Armament @10
2 TIE Interceptors @22
4 TIE Fighers @32
TOTAL: 400 points

And mini-sized into a 300 pointer:

Gladiator I @56 + Demolisher @10 + Engine Techs @8
Gladiator I @56 + Insidious @3 + Engine Techs @8
Victory I @73 + Screed @26 + Enhanced Armament @10
3 TIE Interceptors @33
2 TIE Fighers @16
TOTAL: 299 points

The Victories (or Victory in the cheaper version) are zoners, locking down objectives (e.g. in Fire Lanes) and/or forcing the opponent to go where you want them to go. Meanwhile, the Gladiators rush down the opponent, using their supreme speed and maneuverability (with Engine Techs and the Demolisher title on one) to lay down some seriously punishing firepower (enhanced by Screed and Expanded Launchers on one). When Wave 2 comes out, I would probably find a way to add in Rapid Reload (+1 black on each side). The fighters are merely speed bumps, but this list has enough Squadron rating to use them as a first-strike force that can hopefully take down about two of the opponent's fighters before they get to shoot back.

Objectives: Advanced Gunnery, Fire Lanes, and Dangerous Territory

IMHO you've spent too much points for upgrades and too little for fighter screen in your 400 pts roster. First to drop are Enhanced armaments.

I have far more faith in the demolisher getting to use its launchers than the insidious

plus, a single attack with 4 blacks and 2 reds will probably still oneshot at least a corvette

how many more fighters should he take? and why?

The rebel player can use max 10 squadrons (12 in A-wing-only starfighter wing but it's improbable) so I would use 10 TIEs (8 if I really really need those upgrades) to tie (pun intended) their assets for a while and reduce their numbers.

I do not find that the black dice on the Victory I get used much (or ever in all the games I have played with them) and find "upgrading" to the Victory II much more useful. Just my two cents.