When starting to grow, I'd suggest you look for a decent used evaporator, but if soldered be sure it is lead free, rather than getting one built by someone, especially if they are not real familiar with evaporators. But that's just me. Do you have any slope where the trees are? If you even only have 8-10' of slope, I'd suggest using 3/16 lateral lines and collect them in as few tanks as possible, 1 is best but not always possible or feasible without vacuum. Then get a sap pump and pump the sap from the tank(s) to where you will boil. A 1" gas powered pump and a 1" black poly pipe will move lots of sap.
Then if you outgrow whatever evaporator you get, look for a bigger one just after the season ends, that is when you will get the best prices, new or used.
As far as sugarhouses go, I built a 16x24 after my first season thinking I may eventually get to 250-300 taps. I then got a used 2x6 and it fit well. I kept growing and before I knew it I outgrown the evap. At that point I should have gotten an RO, but I found a 3x8 evap. at a great price so I bought that. It fit in the sugarhouse OK but things were getting crowded. I had added a filter press, a 16x24" bottler and a 16x34 finisher. I now will have about 1450 taps this coming season (remember, I was only going to grow to 250-300) and I bought a new set of pans for my 3x8 arch. I since have added a 250 GPH RO and my finisher now is 2'x6'. The little 16'x24' sugarhouse is now real cramped. I really need to expand but life keeps getting the way.