The bike should be good enough to do the trip, although I wouldn't classify in the "reasonably good" category as you do. A few things to look at changing to do such riding which won't cost much money:

First, I assume you're going to be primarily riding on the roads or paved trails, but it looks like the bike has 26-inch wheels, and so probably has trail-ready tyres: knobbly, about 2 inches wide and with tyre pressures of about 50 psi. Instead, I would replace those with some smoother 1.5-inch wide tyres pumped up to 70 psi, which will be MUCH more efficient.

Second, do some long test rides, not only to improve fitness, but also to test whether the saddle is suitable for spending many hours in it. Generally, you don't want something that is too soft (softer is not always better), although you certainly don't want racing-hardness. However, saddles are a very personal thing.

Third, put some bar-ends on the handlebars if you haven't already got them. Everyone who tours with straight bars without any extensions complains of hand numbness. The way to avoid this is to give yourself multiple hand positions to use. The straight bar is somewhat limiting in this respect compared to butterfly bars or drop bars, but if you get a set of bar-ends then that will give you an extra hand position, and if you get some really long ones (like these) then you may be able to get a third, with your hands at the ends and your wrists resting on the grips.

Regarding editing posts, you'll be able to do so after you've made at least 5 posts and been a member for at least one week (I believe).