1) Yes, you can put longer term, but your stamp duty will be higher. One of the ways is you put one year but the tenant has the option to continue renting with the agreed amount (same amount or increase by how many percent).

2) You can actually put more than that. But depend, if tenant will able to find cheaper one or places more convenient to them, they may move after the minimum period. The option will not cost anything to them.

It is good that you sign another agreement after the earlier one end, or else the tenant has the freedom to move out or not paying you because no more agreement bound.

1) one (1) year + one (1) year [optional] is the norm currently being practiced in the market and you can depart from the norm and imposes either two (2) or three (3) years on the principal period and with an option of either one (1), two (2) or three (3) but never three (3) simply because any period more than three (3) years continuously amounts to a lease, you don't want to lease your property.

2) you can go to a maximum of hundred (100) years if the parties have not issues but noted my paragraph (1) on the issue of lease and also, limitation period sets in after six (6) years. the only good thing you get out of having long extendable option periods is that you don't need to redraft a new tenancy agreement, all you need to do is have a letter to confirm the exercise of the option and then have it stamped ad valorem.

3) you are right, if you have a two (2) years + two (2) years tenancy agreement, once the entire four (4) years period has lapsed then you need to prepare a fresh tenancy agreement.