If your only doing two 30 day stays and one 60 day. You could just get the visa on entry for the 30 and a tourist visa (60 days) for the 60 day stay. You need the tourist visa before travelling. All can be extended at immigration. You can get the tourist visa on line as far as I know. If you stay with in your planned times, you wouldn't need to go near immigration
If your doing 3 months get a tourist visa (60 + 30days via immigration) for your long stay. You get in home country before fly. 30 day other holiday get your visa on arrival. Shouldn't be a problem
If you use an agent it might be easier, but if they do it under the counter and you decide to go on your own in the future, you could find yourself with all sorts of problems.