You’re correct that the initial company draft is the only random part of the game.
The most difficult recalculating of routes is when you shift from a bunch of 2 trains to permanent trains. Some track exists primarily to ensure, say, B&O can run to Wheeling twice for the steamboat company or NYC can run to Cleveland twice, and then becomes useless until you can get two permanent trains.
The biggest advantage to starting a second company is that you create a bunch of money from nowhere to buy permanent trains (you can raise a lot of capital by issuing shares) and those trains can be bought across to the ‘correct’ company (preferably the one where you’re making a greater margin than your opponents on the dividends!)
The most common “usually smart” thing I see newbies avoid is issuing shares to the stock market in the first operating round. If no one bought your shares (because your share value was really expensive or whatever) you probably want at least one or two in there BEFORE the value drops at the end of the first operating round so you have more money to throw around on trains or buying in private companies.
The second common mistake is only buying a single 2 train - that’s what happened to Amanda’s PRR at Unplugged. She was stuck in stasis where she couldn’t make enough money to increase PRR’s stock value, no one wanted to buy in because revenues were low. She only had two PRR shares, so at most PRR could raise another $180 or so by putting two more in the stock market. It was… a lot like that game of Saint Petersburg we played at the party, actually.
The third common mistake is spending a lot on privates in the initial draft, and then failing to recoup that initial investment before the second stock round. I always want my corporation to pay me at least enough to get an extra share in the second stock round, but new players usually won’t buy in any privates before the second stock round. Less money tied up in the corporation is more money to reinvest.
For those who are interested, this is the review that made me invest in learning this game in the first place:
1846 — a fine introductory game in the 18XX series