I want to solve a differential equation of second order with complex initial conditions. However, to simplify the problem, I made it to a first order differential equation. Nonetheless, I am still facing some problems I might want to review here. The code is as follows:

    ode1 = x''[t] + 3 x'[t] Sqrt[(x'[t])^2/6 + (1 - Exp[-x[t] Sqrt[2/3]])^2/4] + Sqrt[3/2] Exp[-x[t] Sqrt[2/3]] (1 - Exp[-x[t] Sqrt[2/3]]) == 0
    ode1IC = {x'[0] == -0.008226306418212731, x[0] == 5.630991866033891};
    solX = NDSolve[{ode1, ode1IC}, x, {t, 0, 500}][[1, 1]]
    ode2 = a'[t]/a[t] == Sqrt[(x'[t])^2/6 + (1 - Exp[-x[t] Sqrt[2/3]])^2/4];
    ode2 = ode2 /. solX;
    ode2IC = a[0] == 1;
    sola = NDSolve[{ode2, ode2IC}, a, {t, 0, 500}][[1, 1]]
    ode3 = \[Tau]'[t] == 1/a[t];
    ode3 = ode3 /. sola;
    ode3IC = \[Tau][149.4517772937791] == 0;
    solTao = NDSolve[{ode3, ode3IC}, \[Tau], {t, 0, 500}][[1, 1]]
    f = ((7.41193*10^6)^2 - ((3/2 + 1/2*((Sqrt[3/2] Exp[-x[t] Sqrt[2/3]] (1 - Exp[-x[t] Sqrt[2/3]]))/(3/4 (1 - Exp[-x[t] Sqrt[2/3]])^2))^2 + 1/2 ((Exp[-Sqrt[8/3] x[t]] (1 - Exp[Sqrt[2/3] x[t]] (1 - Exp[-Sqrt[2/3] x[t]]))/(3/4 (1 - Exp[-x[t] Sqrt[2/3]])^2))))^2 -- 1/4)/(\[Tau][t])^2) /. solX;
    ode4 = u''[t] + f*u[t] == 0;
    ode4 = SetAccuracy[(Solve[ode4, u''[t]] /. Rule -> Equal)[[1, 1]] // 
    Simplify, Infinity];
    ode4 = ode4 /. {solTao, solX};
    ic={u[0]==0.000259728 E^(I (-0.0249668)),u'[0]==1925.09 E^(I (-1.59576))};
    ic=SetAccuracy[ic,Infinity];
    sol = DSolveValue[{ode4, ic}, u[t], t];

There seems to be no plot for $f(t)$, and the solution is not given for $u''(t)+f(t)u(t)=0$.

First Error:

    Solve::inex: Solve was unable to solve the system with inexact coefficients or the system obtained by direct rationalization of inexact numbers present in the system. Since many of the methods used by Solve require exact input, providing Solve with an exact version of the system may help.