It's occurred a bit more recently than in the past. If this is a sign that the forums is getting busier I see this as a good thing.
An occasional hiccup is ot going to deter those of us who've been members for a while, but it will definitely put off someone who follows a link to the forum for the first time and gete the unavailable message. It will put them off even more if they try again on a couple of other occasions.
So, from the point of view of building the forum it is a serious problem indeed.
As for your fonts - it won't affect anything at all, bandwidth wise - changing any attribute is the same as adding a few letters before and a few letters after the phrase you have emboldened or whatever.
However, posting in big fonts or bold fontsl, like typing in CAPITALS, is looked upon as the equivalent of shouting. So it's great if you want to add emphasis to a particular word or statement. Posting whole posts in large colourful fonts therefore looses impact and, worse, it can give the impression the poster is full of their own importance. This is almost certainly the opposite of the desired effect of the poster who is just trying to be jovial!
There are two paths you can go by, but in the long run there's still time to change the road you're on