According to Dave Walker, owner of Emerald ECU and very exerpeicned dyno operator says no. It makes little to no difference in power. He tried it. It is mainly done for emissions reasons. As your ECU runs a cam phase sensor, it is of no extra cost or effort to do sequential. So no reason to not use it. This will stay a theoretical argument.
The term "little" could be interpreted wrong. The question is, is it worth full sequential in terms of power and efficiency?
If you have trouble finding methanol compatible injectors, you might consider ethanol instead. It makes surprisingly little difference and ethanol compatible injectors are plently around. From a chemistry standpoint, any injector that is fully ethanol compatible should also last with methanol. Worst case buy one, soak in in Methanol in a jar and try if it still works once a month.
Could do but a little risky in reality.
If you go for the 350 range, you need huge injectors anyhow. For 350HP on petrol alone you already need 650cc injectors. On e85 more like a 1000cc a minute and with methanol you are heading in the 1300cc/min direction. (Numbers just scaled up, not calculated and for a 4 cylinder engine) your intake valve is open for about 70% of the revolution with the intake stroke for a 270 deg cam. So once you injector duty cycle exceeds 70% you are injecting against a closed valve anyhow. It does not really matter anyhow.
You are right but you are forgetting that if I go direct port injection I will be working with 8Injectors. Four will be used as pump fuel and four will be water/methanol. Injectors flowrates will change drastically. Also I am planning running a high pressure pump (trying to find 300psi+)
If you want to maximize in cylinder charge cooling from methanol, you need in cylinder direct injection with those nice 150 bar injectors. No more valve wetting. Thing is you still need to carefully position them to minimize the spray hitting the surfaces in the cylinder. Any spray hitting the walls just cools the metal and not the air.
In one of the papers I linked in the literature section of this forum quantifies the effect of this internal cooling by comparing at which IAT a engine starts to knock running either direct injection of port injection. They employed gasoline and ethanol.
I believe 150Bar is above and beyond 
If the car is a daily driver, I'd seriously consider a dual fuel system. Run it on petrol and phae over to alcohol or e85 on boost (plus option water, if requiered). Ronin aka Frank Profera did such a dual fuel system with his 680HP Lotus Exige (the Ronin RS 211) running a turbocharged 1.8l 2ZZ-GE, it's "original" engine. He uses isopropanol in a secondary injection system. Ethanol would work as well, but isopropanol is easier to come by in the US in any drug store.
Pothole along on 95 octane and inject the 110 stuff on demand. A little 10l fuel cell should do.
That's the Aim